ci/docs: enable dispatch build without warning as errors (#19948)

Author: Borda

.github/workflows/docs-build.yml

@@ -108,11 +108,14 @@ jobs:
       - name: Full build for deployment
         if: github.event_name != 'pull_request'
         run: echo "DOCS_FETCH_ASSETS=1" >> $GITHUB_ENV
+      - name: Build without warnings
+        if: github.event_name != 'workflow_dispatch'
+        run: echo "BUILD_SPHINX_OPTS=-W --keep-going" >> $GITHUB_ENV
       - name: Make ${{ matrix.target }}
         working-directory: ./docs/source-${{ matrix.pkg-name }}
         # allow failing link check and doctest if you run with dispatch
-        continue-on-error: ${{ (matrix.target == 'doctest' || matrix.target == 'linkcheck')  && github.event_name == 'workflow_dispatch' }}
-        run: make ${{ matrix.target }} --debug --jobs $(nproc) SPHINXOPTS="-W --keep-going"
+        continue-on-error: ${{ (matrix.target == 'doctest' || matrix.target == 'linkcheck') && github.event_name == 'workflow_dispatch' }}
+        run: make ${{ matrix.target }} --debug --jobs $(nproc) SPHINXOPTS="$BUILD_SPHINX_OPTS"
 
       - name: Keep artifact
         if: github.event_name == 'pull_request'