ci: fix docs workflow using cache

.github/workflows/docs.yml

@@ -10,21 +10,22 @@ on:
   # Allow manual trigger (workflow_dispatch)
   workflow_dispatch:
 
-permissions:
-  contents: write
-
 jobs:
   get_cache_key:
     runs-on: ubuntu-latest
+    outputs:
+      cache_key: ${{ steps.set_cache_key.outputs.cache_key }}
     steps:
-      - run: echo "cache_key=docs-build-$(date --utc '+%V')" >> $GITHUB_ENV
+      - name: Set cache key
+        id: set_cache_key
+        run: echo "cache_key=docs-build-$(date --utc '+%V')" >> $GITHUB_OUTPUT
 
   build_doxygen:
     uses: hotosm/gh-workflows/.github/workflows/doxygen_build.yml@main
     with:
       cache_paths: |
         docs/apidocs
-      cache_key: ${{ env.cache_key }}
+      cache_key: ${{ steps.get_cache_key.outputs.cache_key }}
 
   build_openapi_json:
     uses: hotosm/gh-workflows/.github/workflows/openapi_build.yml@main
@@ -33,7 +34,7 @@ jobs:
       example_env_file_path: ".env.example"
       cache_paths: |
         docs/openapi.json
-      cache_key: ${{ env.cache_key }}
+      cache_key: ${{ steps.get_cache_key.outputs.cache_key }}
 
   publish_docs:
     uses: hotosm/gh-workflows/.github/workflows/mkdocs_build.yml@main
@@ -42,4 +43,4 @@ jobs:
       cache_paths: |
         docs/apidocs
         docs/openapi.json
-      cache_key: ${{ env.cache_key }}
+      cache_key: ${{ steps.get_cache_key.outputs.cache_key }}