ci: allow tests to be run in forks

Drop the filter on `master`. This prevents us from running the CI on
forked repositories. In particular, it prevents us from pushing
branches to github-forks and have the CI run on them. This is very nice
to have as development tool, as it allows running the real CI without
opening a PR.

.github/workflows/tests.yml

@@ -1,14 +1,6 @@
 name: Tests
 
-# NOTE(mhayden): Restricting branches prevents jobs from being doubled since
-# a push to a pull request triggers two events.
-on:
-  pull_request:
-    branches:
-      - "*"
-  push:
-    branches:
-      - master
+on: [pull_request, push]
 
 jobs:
   pylint: