Cache downloaded packages

Since we're installing poetry after setting up Python we can't
cache the poetry dependencies directly. We can however use its
lockfile as a cache key.

Author: PeterJCLaw

.github/workflows/check.yml

@@ -28,6 +28,8 @@ jobs:
         uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python-version }}
+          cache: pip
+          cache-dependency-path: poetry.lock
 
       - name: Set up Poetry
         uses: abatilo/actions-poetry@v2
@@ -65,6 +67,8 @@ jobs:
         uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python-version }}
+          cache: pip
+          cache-dependency-path: poetry.lock
 
       - name: Set up Poetry
         uses: abatilo/actions-poetry@v2
@@ -102,6 +106,8 @@ jobs:
         uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python-version }}
+          cache: pip
+          cache-dependency-path: poetry.lock
 
       - name: Set up Poetry
         uses: abatilo/actions-poetry@v2