Fix Safari & Safari Technology Preview GitHub Actions runs

We make the epochs' git-push-output have 40 character commit ids,
because actions/checkout allows for ref to be a commit id, but only if
it is exactly a 40 character hex string.

Then, with that fixed, the Safari & Safari Technology Preview runs
should start succeeding, once again able to check code out.

Additionally, fix the `fetch-ref` definition so that it works in the
not-workflow_run case where the output is empty.

Author: gsnedders

.github/workflows/safari_stable.yml

@@ -37,4 +37,4 @@ jobs:
       safaridriver-diagnose: false
       matrix: '{"current-chunk": [1, 2, 3, 4, 5, 6, 7, 8], "total-chunks": [8]}'
       extra-options: --no-fail-on-unexpected
-      fetch-ref: ${{ fromJSON(needs.check-workflow-run.outputs.updated-refs)['refs/heads/epochs/daily'] }}
+      fetch-ref: ${{ fromJSON(needs.check-workflow-run.outputs.updated-refs || '{}')['refs/heads/epochs/daily'] }}

.github/workflows/safari_technology_preview.yml

@@ -37,4 +37,4 @@ jobs:
       safaridriver-diagnose: false
       matrix: '{"current-chunk": [1, 2, 3, 4, 5, 6, 7, 8], "total-chunks": [8]}'
       extra-options: --no-fail-on-unexpected
-      fetch-ref: ${{ fromJSON(needs.check-workflow-run.outputs.updated-refs)['refs/heads/epochs/three_hourly'] }}
+      fetch-ref: ${{ fromJSON(needs.check-workflow-run.outputs.updated-refs || '{}')['refs/heads/epochs/three_hourly'] }}

tools/ci/epochs_update.sh

@@ -43,7 +43,11 @@ main () {
     done
     # This is safe because `git push` will by default fail for a non-fast-forward
     # push, for example if the remote branch is ahead of the local branch.
-    git push --porcelain --tags ${REMOTE} ${ALL_BRANCHES_NAMES} | tee "${RUNNER_TEMP}/git-push-output.txt"
+    # We save the output so that GitHub Actions workflows can find out what got
+    # pushed, as workflows are not triggered by push events caused by another
+    # workflow. We need to pass core.abbrev as actions/checkout only allows refs to
+    # be specified as an object id if they are exactly 40 characters.
+    git -c core.abbrev=40 push --porcelain --tags ${REMOTE} ${ALL_BRANCHES_NAMES} | tee "${RUNNER_TEMP}/git-push-output.txt"
 }
 
 cd $WPT_ROOT