style(github): clarifies workflow naming

.github/workflows/_build-push-test.yml → .github/workflows/_backstop-docker-ci.yml

@@ -1,7 +1,13 @@
-name: 🙈 Build, Push, and Test
+name: 🙈 Backstop & Docker CI
+run-name: "🙈 CI running on ${{ github.event_name == 'pull_request' && format('PR #{0}: {1}', github.event.pull_request.number, github.event.pull_request.title) || format('latest {0}', github.ref_name) }}"
+# Tests backstopjs alone, docker build, docker push to
+# ghcr.io, docker pull from ghcr.io, and backstopjs in
+# the docker docker build.
 
 on:
   workflow_dispatch:
+  pull_request:
+    branches: [master, develop]
 
 permissions:
   checks: write