Fix warnings in checkspelling test

[waylan]

The checkspelling test recently started raising a bunch of warnings (see an example here) which all are related a the documentation. As the build is done in strict mode, the test always fails. We need to go through the various warnings and address them and consider possibly removing strict mode. After all, the warnings are not related to spelling and shouldn't be causing the checkspelling test to fail. Perhaps an additional test could be added which would build the docs in strict mode if we care about that??