chore(deps): update actions/cache action to v4

Author: renovate[bot]

.github/workflows/documentation.yml

@@ -36,7 +36,7 @@ jobs:
         with:
           python-version: '3.9'
 
-      - uses: actions/cache@v3
+      - uses: actions/cache@v4
         with:
           key: ${{ github.ref }}
           path: .cache

.github/workflows/publish-to-test-pypi.yml

@@ -24,7 +24,7 @@ jobs:
         with:
           python-version: '3.9'
 
-      - uses: actions/cache@v3
+      - uses: actions/cache@v4
         with:
           key: ${{ github.ref }}
           path: .cache