Run Tests on PRs regardless of base branch (#46)

`branches: ['*']` looks like "all branches", but in GitHub's [filter
pattern
syntax](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#filter-pattern-cheat-sheet)
the `*` glob does not match `/` — and `pull_request.branches` filters on
the *base* branch. So the Tests workflow silently skipped any PR whose
base branch contains a slash. Concretely: #45 is stacked on #42's
`claude/...` branch and got no Tests run at all.

Drop the filter — a bare `pull_request:` trigger covers every base
branch. (`'**'` would too, but no filter says what it means.) The
README's example workflows never had a filter, so no doc change is
needed beyond the inline comment.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01JHvKryT4QUpHYdNq9YEQxX

---
_Generated by [Claude
Code](https://claude.ai/code/session_01JHvKryT4QUpHYdNq9YEQxX)_

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

Author: Phlogistique

.github/workflows/tests.yml

@@ -2,7 +2,6 @@ name: Tests
 
 on:
   pull_request:
-    branches: ['*']
 
 jobs:
   unit-tests: