workflows/pr-comment,run-kola: fix concurrency + results comment

This change includes 2 unrelated small fixes to the "PR comment command"
build+test feature:

1. The concurrency group now contains the PR number, ensuring that
   builds for multiple PRs can run in parallel. This addresses an issue
   in which starting a build on a PR would cancel a running build of
   another PR.
2. Post test results to the PR where the build command was issued on.
   The add-pr-comment step's condition was not updated when switching
   to PR comment commands for starting builds, so the step would only
   run if the action was triggered by a PR change event. Since we now
   trigger on issue_comment, the step never ran.

Signed-off-by: Thilo Fromm <thilofromm@microsoft.com>

.github/workflows/pr-comment-build-dispatcher.yaml

@@ -7,7 +7,7 @@ permissions:
   pull-requests: write
 
 concurrency:
-  group: ${{ github.workflow }}-pr-command-${{ github.head_ref || github.ref_name }}
+  group: ${{ github.workflow }}-pr-command-${{ github.event.issue.pull_request.number }}
   cancel-in-progress: true
 
 jobs:

.github/workflows/run-kola-tests.yaml

@@ -351,8 +351,9 @@ jobs:
 
           cat test-results.md >> "$GITHUB_STEP_SUMMARY"
 
-      - name: If started from a PR, post test summary to PR
-        if: ${{ github.event_name == 'pull_request' }}
+      - name: If started from a PR event or a PR comment command, post test summary to PR
+        if: ${{ github.event_name == 'pull_request' || github.event.issue.pull_request }}
         uses: mshick/add-pr-comment@v2
         with:
+          issue: ${{ github.event.pull_request.number || github.event.issue.pull_request.number }}
           message-path: "scripts/test-results.md"