Stop Sphinx from complaining about missing Doxygen files in CI

.github/workflows/docs-test.yml

@@ -33,6 +33,9 @@ jobs:
       - name: Build docs
         run: |
           cd Docs/
+          # remove missing TOC entries that would otherwise be generated by
+          # doxygen to avoid warnings about missing references
+          sed -i -e 's/^   filelist$//; s/^   classlist$//' source/index.rst
           make SPHINXOPTS='-v -W --keep-going' NO_DOXYGEN=TRUE html
 
       - name: Check links