add requirements.txt for mkdocs

.github/workflows/build_docs.yml

@@ -16,16 +16,15 @@ jobs:
         with:
           python-version: 3.9
 
-      - name: Set Cache ID Based on UTC Week Number
-        run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV
-
       - name: Cache dependences
         uses: actions/cache@v3
         with:
-          key: mkdocs-material-${{ env.cache_id }}
-          path: .cache
+          path: ~/.cache/pip
+          # Unique cache key based on requirements.txt in docs directory
+          key: ${{ runner.os }}-pip-${{ hashFiles('docs/requirements.txt') }}-mkdocs-deps 
+          # Restore partial cache if exact match is not found
           restore-keys: |
-            mkdocs-material-
+            ${{ runner.os }}-pip-  
 
       - name: Install mkdocs and dependencies
         run: |

docs/requirements.txt

@@ -0,0 +1,5 @@
+mkdocs<=1.6.0
+mkdocs-material<=9.5.23
+mkdocs-open-in-new-tab<=1.0.3
+mkdocstrings<=0.25.1
+mkdocstrings-python<=1.10.2