[CI] Use doxygen 1.9.4 - Githubissues

Changes proposed in this pull request

Using doxygen 1.9.4 to build online documentation resolves an issue with broken links.

Closes #1592

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Checklist

[ ] The pull request includes a clear description of this code change
[ ] Commit messages have short titles and reference relevant issues
[ ] Build passes (scons build & scons test) and unit tests address code coverage
[ ] Style & formatting of contributed code follows contributing guidelines
[ ] The pull request is ready for review

Cantera / cantera