ci: run full test suite on changes to pyproject.toml

We had a rule for requirements-dev.txt, but now we have switched
to pyproject.toml for dependencies, we need to run tests on changes
to that.

PR #4999

.github/workflows/tests.yml

@@ -5,11 +5,11 @@ on:
   pull_request:
     paths:
       - '**.py'
-      - 'requirements-dev.txt'
+      - 'pyproject.toml'
   push:
     paths:
       - '**.py'
-      - 'requirements-dev.txt'
+      - 'pyproject.toml'
 
 jobs:
   tests: