Run pip install unconditionally in CI workflow (#1626)

The cache is not guaranteed to be complete or up to date. The CI workflow is currently not running any of the Python tests because of a missing Numpy package.

.github/workflows/build-ci.yml

@@ -123,7 +123,6 @@ jobs:
         restore-keys: ${{ runner.os }}-py${{ matrix.python-version }}-mpi-${{ matrix.enable-mpi }}-pip-
 
     - name: Install Python dependencies
-      if: steps.cache.outputs.cache-hit != 'true'
       run: pip install -r python/requirements.txt
 
     - name: Install mpi4py
@@ -161,4 +160,4 @@ jobs:
       if: failure()
       with:
         name: py${{ matrix.python-version }}-tests-mpi-${{ matrix.enable-mpi }}-log
-        path: ${{ github.workspace }}/build/meep-${{ env.MEEP_VERSION }}/_build/sub/python/test-suite.log
+        path: ${{ github.workspace }}/build/meep-${{ env.MEEP_VERSION }}/_build/sub/python/test-suite.log