ci: Run docstring tests again (#2576)

This comparison expression has always been broken.

However in #2334 it changed from `!= 'true'` to `== 'false'`.
So the tests went from always running to never running.

.github/workflows/ci-cd.yml

@@ -108,7 +108,7 @@ jobs:
         run: pytest -v
 
       - name: Run docstring tests
-        if: github.event.pull_request.head.repo.fork == 'false'
+        if: github.event.pull_request.head.repo.fork == false
         env:
           MODAL_ENVIRONMENT: client-doc-tests
           MODAL_TOKEN_ID: ${{ secrets.MODAL_TOKEN_ID }}
@@ -243,4 +243,4 @@ jobs:
         env:
           TWINE_USERNAME: __token__
           TWINE_PASSWORD: ${{ secrets.PYPI_API_TOKEN }}
-        run: twine upload dist/* --non-interactive
+        run: twine upload dist/* --non-interactive