Move build_tools unit tests to a standalone workflow file (#3076)

## Motivation

I'm adding a new unit test in #3057
that validates our github actions workflows. I want that test to run
when any workflow file is modified and to be a "required check" that
blocks merging. Our current filtering via
[`configure_ci.py`](https://github.com/ROCm/TheRock/blob/main/build_tools/github_actions/configure_ci.py)
has various exclusions that skip running the existing
"build_*_artifacts.yml" workflows if only "skippable paths" or "files
unrelated to CI" are modified. Rather than extend the filtering there, I
figured a standalone workflow file that always runs would be more
natural.

## Technical Details

* The new `unit_tests_summary` job gives us an anchor point that depends
on all unit test jobs (currently just the Linux and Windows matrix jobs)
to use as a required check.
* The `toJson()` code in that job is forked from the similar step in
ci.yml. Yes, it's gross. Yes, I want to move it to a reusable workflow
or script.
* Creating a standalone workflow like this will also
1. Exclude these tests from workflow runs in rocm-libraries /
rocm-systems
2. Keep these tests included when we switch from
[`ci.yml`](https://github.com/ROCm/TheRock/blob/main/.github/workflows/ci.yml)
to
[`multi_arch_ci.yml`](https://github.com/ROCm/TheRock/blob/main/.github/workflows/multi_arch_ci.yml)
* Unit tests use standard github-hosted runners and take 1 minute on
average. If we add tests that depend on self-hosted runners in some way
we could switch them over.
* Setting `GITHUB_TOKEN: ${{ github.token }}` in the env allows these
tests to run:
https://github.com/ROCm/TheRock/blob/901d88d25b246cd3af1405179b6acc31f435eb02/build_tools/github_actions/tests/github_actions_utils_test.py#L21-L29

## Test Plan

Tested in my fork:
* With tests passing:
https://github.com/ScottTodd/TheRock/actions/runs/21300728642
* With tests failing:
https://github.com/ScottTodd/TheRock/actions/runs/21300780457

Tested on this PR:
https://github.com/ROCm/TheRock/actions/runs/21368145938?pr=3076

## Test Result

Test workflow runs succeeded and failed as expected.

## Submission Checklist

- [x] Look over the contributing guidelines at
https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.

Author: ScottTodd

.github/workflows/build_portable_linux_artifacts.yml

@@ -105,10 +105,6 @@ jobs:
         run: |
           ./build_tools/health_status.py
 
-      - name: Test build_tools
-        run: |
-          python -m pytest build_tools/tests build_tools/github_actions/tests
-
       - name: Fetch sources
         timeout-minutes: 30
         run: |

.github/workflows/build_windows_artifacts.yml

@@ -113,10 +113,6 @@ jobs:
           ccache --zero-stats
           python ./build_tools/health_status.py
 
-      - name: Test build_tools
-        run: |
-          python -m pytest build_tools/tests build_tools/github_actions/tests
-
       # TODO: We shouldn't be using a cache on actual release branches, but it
       # really helps for iteration time.
       - name: Enable cache

.github/workflows/unit_tests.yml

@@ -0,0 +1,72 @@
+name: Unit Tests
+
+on:
+  push:
+    branches:
+      - main
+      - release/therock-*
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  unit_tests:
+    name: "Unit Tests :: ${{ matrix.runs-on}}"
+    strategy:
+      fail-fast: false
+      matrix:
+        runs-on: [ubuntu-24.04, windows-2022]
+    runs-on: ${{ matrix.runs-on }}
+    defaults:
+      run:
+        shell: bash
+    env:
+        GITHUB_TOKEN: ${{ github.token }}
+
+    steps:
+    - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+    - uses: actions/setup-python@83679a892e2d95755f2dac6acb0bfd1e9ac5d548 # v6.1.0
+      with:
+        python-version: 3.12
+
+    - name: Install python deps
+      run: pip install -r requirements-test.txt
+
+    # Note: build_tools/github_actions/ contains complicated tests in some
+    # subdirectories that do not support pytest:
+    #   build_tools/github_actions/benchmarks/scripts/
+    #   build_tools/github_actions/test_executable_scripts/
+    # We could move them if we want a simple `pytest build_tools/` to work.
+    # TODO(scotttodd): enable code coverage collection/reporting here
+    - name: Test build_tools
+      run: |
+        python -m pytest -vv \
+          build_tools/tests \
+          build_tools/github_actions/tests
+
+  # TODO(scotttodd): share code with ci_summary in ci.yml
+  #   Could reuse this from prior projects:
+  #   https://github.com/iree-org/iree/blob/main/.github/workflows/workflow_summary.yml
+  #   (including support for sending alerts on failures)
+  unit_tests_summary:
+    name: Unit Tests Summary
+    if: always()
+    needs:
+      - unit_tests
+    runs-on: ubuntu-24.04
+    steps:
+      - name: Output failed jobs
+        run: |
+          echo '${{ toJson(needs) }}'
+          FAILED_JOBS="$(echo '${{ toJson(needs) }}' \
+            | jq --raw-output \
+            'map_values(select(.result!="success" and .result!="skipped")) | keys | join(",")' \
+          )"
+          if [[ "${FAILED_JOBS}" != "" ]]; then
+            echo "The following jobs failed: ${FAILED_JOBS}"
+            exit 1
+          else
+            echo "All required jobs succeeded."
+          fi