ci: Avoid suggesting unnecessary baseline updates (#37158)

When checking for baselines that need updating due to fixed issues, we
ignore the "issue statistics" comment at the top of the file so as to
not make people have to update the baselines unnecessarily.

However, if one project has a real update needed while a different one
has only comments, we're still instructing the author to update both of
them even though only the former is needed.

Let's not do that.

.github/workflows/tests.yml

@@ -327,14 +327,19 @@ jobs:
           pnpm jetpack phan --all -v --format github
       - name: Check baselines
         run: |
-          # Anything changed (with a side of printing the diff)
+          # Anything changed? (with a side of printing the diff)
           if git diff --exit-code --ignore-matching-lines='^    // ' -- .phan/baseline.php '*/.phan/baseline.php'; then
             exit 0
           fi
 
           # Collect which projects changed to suggest the right command.
           PROJECTS=()
           for f in $( git -c core.quotepath=off diff --name-only -- .phan/baseline.php '*/.phan/baseline.php' ); do
+            # --name-only and --ignore-matching-lines don't combine, so we have to do the check separately.
+            if git diff --quiet --exit-code --ignore-matching-lines='^    // ' -- "$f"; then
+              continue
+            fi
+
             if [[ "$f" == ".phan/baseline.php" ]]; then
               SLUG=monorepo
             elif [[ "$f" == projects/*/*/.phan/baseline.php ]]; then