Fix CI push-trigger path filter: test/** -> tests/**

The tests workflow's push trigger filtered on src/**, test/**,
setup.py, requirements.txt, and Makefile -- but the actual test
directory is tests/** (plural), so pushes touching only tests/
never queued a CI run at all. Caught while iterating on tests/
test_importer.py: the fix-up commit for that file needed a PR
just to get any CI run at all.

Author: jaltmayerpizzorno

.github/workflows/tests.yml

@@ -4,7 +4,7 @@ on:
   push:
     paths:
       - src/**
-      - test/**
+      - tests/**
       - setup.py
       - requirements.txt
       - Makefile