Use git rev-parse to get master version (#78)

Blocked on: runtimeverification/devops#234
Blocked on:
runtimeverification/mir-semantics#561

This uses `git rev-parse` instead of relying on github action variables
to get the version to push, as the prior attempt didn't end up including
the label.

Author: ehildenb

.github/workflows/master.yml

@@ -23,7 +23,7 @@ jobs:
       - name: 'Update dependents'
         run: |
           set -x
-          VERSION=${{ github.event.push.head.sha }}
+          VERSION=$(git rev-parse HEAD)
           curl --fail                                                          \
             -X POST                                                            \
             -H "Accept: application/vnd.github+json"                           \