I fixed the mistake you pointed out in build.sh

> It would be nice to have syntax highlighting and indentation tests for
> this (ideally covering everything). If you're interested, take a look
> at go-ts-mode-tests.el and the files it references for inspiration.

I wrote some simple tests for both go-mod-ts-mode and go-work-ts-mode.
For syntax highlighting, I had them both use the same file
(font-lock-package.go), since they have some compatible elements, and
for indentation, I made a simple test for indenting multiple lines.

I also changed the face for operators (on go-work-ts-mode), as I
incorrectly used font-lock-warning-face.

Also, please let me know your opinion on how I layed out the grammars in
the commentary section. I think I'll go through the other tree-sitter
modes and add the grammar to their commentary section too, so it's nice
to get some feedback before making these changes.