Pin pip version in update requirements GitHub Action workflow (#2983)

.github/workflows/update-requirements.yml

@@ -27,6 +27,11 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
           cache: pip
+        # Workaround a current issue with `pip check`.
+        # See: https://github.com/stanford-crfm/helm/issues/2855
+        # TODO(#2855): Remove this
+      - name: Use old pip
+        run: pip install --upgrade pip~=24.1.2
       - name: Install PyTorch manually
         # PyTorch has to be installed manually in a separate step with --no-cache-dir
         # to avoid pip getting killed because PyTorch is too big