Revert "[CI] Only run one post commit job on a push to a pull request…

… in sycl-devops-pr" (#16092)

Reverts #16079

This is cancelling jobs in unexpected ways, I need to debug it and fix
the problem.

.github/workflows/sycl-post-commit.yml

@@ -20,11 +20,8 @@ on:
     - ./devops/actions/cached_checkout
 
 concurrency:
-  # Cancel a currently running workflow from the same PR or commit hash.
-  # We need to use the user's branch name (which is in different variables
-  # for pull request events and push events) so that making a PR from a
-  # sycl-devops-pr branch doesn't cause two postcommit runs.
-  group: "${{ github.actor }}-${{ github.head_ref || github.ref_name }}"
+  #  Cancel a currently running workflow from the same PR or commit hash.
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.sha }}
   cancel-in-progress: true
 
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