talkatu/talkatu

Convert all of the unit tests to GTK4
gtk4
2022-01-31, Gary Kramlich
9dc271918fe6
Convert all of the unit tests to GTK4

Testing Done:
Compiled each test by itself. They still error out because of `TalkatuScrolledWindow` but thats the only error now.

Reviewed at https://reviews.imfreedom.org/r/1265/
Talkatu is versioned in [mercurial](https://www.mercurial-scm.org/) and is
available on [keep.imfreedom.org](https://keep.imfreedom.org/talkatu/talkatu).
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