fix: use actions/cache@v4 tag instead of specific hash

- Remove specific hash reference for actions/cache to use latest v4

Author: thegdsks

.github/workflows/docs.yml

@@ -33,7 +33,7 @@ jobs:
           python-version: '3.11'
 
       - name: Cache pip dependencies
-        uses: actions/cache@6849a6489940f00c2f30c0fb92c6274307ccb58a # v4.1.2
+        uses: actions/cache@v4
         with:
           path: ~/.cache/pip
           key: ${{ runner.os }}-pip-${{ hashFiles('requirements.txt') }}