ci(digest): run CI on push to ci/upstream-digest branch (#53)

Problem: GITHUB_TOKEN-created PRs suppress pull_request triggers,
so CI never runs and auto-merge stalls.

Solution: add ci/upstream-digest to the push trigger in test and
quality workflows. CI runs on the branch push before the PR exists;
check results attach to the commit SHA so the PR sees them as
passing. The digest workflow reverts to GITHUB_TOKEN for PR
creation — no PAT needed, no contribution inflation.

.github/workflows/test.yaml

@@ -4,7 +4,7 @@ on:
   pull_request:
     branches: [main]
   push:
-    branches: [main]
+    branches: [main, ci/upstream-digest]
 
 jobs:
   test: