Reduce OS variants (#965)

* concepts.wip exercises changed to deprecated

* Revert "concepts.wip exercises changed to deprecated"

This reverts commit 28f91a8.

* Change annelyns-infiltration slug for old version

* Revert "Change annelyns-infiltration slug for old version"

This reverts commit 09dfe5d.

* runs only on Ubuntu

---------

Co-authored-by: Colin Leach <[email protected]>

Author: colinleach

.github/workflows/exercise-tests.yml

@@ -17,13 +17,12 @@ on:
 
 jobs:
   test:
-    name: Julia ${{ matrix.julia-version }} - ${{ matrix.os }}
-    runs-on: ${{ matrix.os }}
+    name: Julia ${{ matrix.julia-version }} - ubuntu-24.04
+    runs-on: ubuntu-24.04
     strategy:
       fail-fast: false
       matrix:
         julia-version: ["1.10", "1.11", nightly]
-        os: [ubuntu-24.04, windows-2025, macos-15]
 
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
@@ -82,3 +81,4 @@ jobs:
         env:
           RESULTS: ${{ steps.generate-reports.outputs.results-path }}
         shell: julia --color=yes --project {0}
+