Merge pull request #576 from NatLibFi/gh-actions-pip-cache

Enable pip cache in GitHub Actions CI jobs

.github/workflows/python-package.yml

@@ -9,6 +9,9 @@ on:
     - master
   pull_request:
   workflow_dispatch:
+env:
+  PIP_UPGRADE: "true"  # always upgrade to latest version
+  PIP_UPGRADE_STRATEGY: "eager"  # upgrade all dependencies
 jobs:
   test:
     runs-on: ubuntu-latest
@@ -28,9 +31,11 @@ jobs:
       uses: actions/setup-python@v2
       with:
         python-version: ${{ matrix.python-version }}
+        cache: pip
+        cache-dependency-path: setup.py
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pip setuptools wheel
+        python -m pip install pip setuptools wheel
         python -m pip install .[dev]
         python -m nltk.downloader punkt
         # Selectively install the optional dependencies for some Python versions
@@ -74,6 +79,8 @@ jobs:
       uses: actions/setup-python@v2
       with:
         python-version: '3.8'
+        cache: pip
+        cache-dependency-path: setup.py
     - name: Build distribution
       run: |
         python -m pip install wheel