[BUG] Ensure content/keywords and grammars are in sync in main

[Felienne]

Somehow, the keyword files in /content/ and the grammars are not always in sync. For example, currently in main there is a translation of the keywords into Hebrew:

https://github.com/Felienne/hedy/blob/main/content/keywords/he.yaml

But, there is no corresponding grammar file yet:

https://github.com/Felienne/hedy/tree/main/grammars (notice the absence of keywords-he.lark):

This is probably related to the type of thing we have had in other languages too (f.e. https://github.com/Felienne/hedy/pull/3168) I am still not sure of the cause of that issue, but I suspect someone ran the deploy script locally (generating the grammars) and then pushed the generated grammar, but did not also make the change in level 5.

We have already tried to fix this by generating the grammars when deploying: https://github.com/Felienne/hedy/pull/3116 and we also do it when running the tests (both locally and on GitHub) but that does not mean the files also get pushed back to main, so I think we need to do that explicitly when we merge to main?

I am not sure how to create such a hook but I do think we already have that for generating the js files?