ci: again (#966)

.github/workflows/extremes.yml

@@ -92,12 +92,11 @@ jobs:
         run: pytest narwhals --doctest-modules
 
   nightlies:
-    if: github.event_name == 'push'
     strategy:
       matrix:
         python-version: ["3.11"]
         os: [ubuntu-latest]
-
+    if: github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
@@ -119,7 +118,7 @@ jobs:
         run: |
           kaggle kernels output "marcogorelli/variable-brink-glacier"
       - name: install-polars
-        run: pip install *.whl --system
+        run: python -m pip install *.whl
       - name: install-reqs
         run: uv pip install --upgrade tox virtualenv setuptools pip -r requirements-dev.txt --system
       - name: uninstall pyarrow