docs: add cache to PR workflows

`actions/setup-python` poetry cache feature requires poetry to be installed beforehand.
It makes use of it extremely awkward.
That is why `action/cache` is used istead.

Author: dkropachev

.github/workflows/docs-pages.yml

@@ -23,6 +23,16 @@ jobs:
           persist-credentials: false
           fetch-depth: 0
 
+      - uses: actions/cache@v4
+        # actions/setup-python poetry cache feature requires poetry to be installed beforehand
+        # which makes use of it extremely awkward.
+        with:
+          path: |
+            /home/runner/.cache/pip
+            /home/runner/.cache/pypoetry
+          # python and poetry version are in docs/pyproject.toml
+          key: docs-cache-${{ runner.os }}-${{ hashFiles('docs/pyproject.toml', 'docs/Makefile') }}
+
       - name: Set up Python
         uses: actions/setup-python@v6
         with:

.github/workflows/docs-pr.yml

@@ -25,6 +25,16 @@ jobs:
           persist-credentials: false
           fetch-depth: 0
 
+      - uses: actions/cache@v4
+        # actions/setup-python poetry cache feature requires poetry to be installed beforehand
+        # which makes use of it extremely awkward.
+        with:
+          path: |
+            /home/runner/.cache/pip
+            /home/runner/.cache/pypoetry
+          # python and poetry version are in docs/pyproject.toml
+          key: docs-cache-${{ runner.os }}-${{ hashFiles('docs/pyproject.toml', 'docs/Makefile') }}
+
       - name: Set up Python
         uses: actions/setup-python@v6
         with: