ci: temporarily run the tox workflow on push to this branch

Not for merging. `workflow_dispatch` and `schedule` only trigger
workflows that are on the default branch, so the new `tox` workflow
cannot otherwise be run before it is merged. This adds a `push`
trigger limited to this side branch, so pushing the branch runs the
workflow on the fork. No other workflow runs on pushes to it, since
their `push` triggers are limited to `main`.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: EliahKagan

.github/workflows/tox.yml

@@ -4,6 +4,8 @@ name: tox
 # works, including with new releases of tox and virtualenv. That is too slow to
 # run on every push and pull request, so it runs weekly and on demand.
 on:
+  push:
+    branches: [claude/tox-workflow-push-test]  # TEMPORARY: only to test this workflow.
   schedule:
   - cron: "37 5 * * 1"  # Mondays at 05:37 UTC.
   workflow_dispatch: