ci: Add macos-latest to dependency release candidates testing (#1760)

* As seen in Issue #1759, testing pre-releases of software only on Linux
distributions is not enough to catch bugs before they hit in public releases.
To guard against this in the future, add macos-latest to tests for release
candidates on PyPI.

.github/workflows/dependencies-head.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest]
+        os: [ubuntu-latest, macos-latest]
         python-version: ['3.9']
 
     steps: