Link check runs on all languages

[mgeisler]

After merging #2195, I realized that mdbook-linkcheck runs on all languages. This is despite our best efforts in build.yml where we only install the tool on known-good languages:

comprehensive-rust/.github/workflows/build.yml

Lines 150 to 153 in ad9b41c

	- name: Install mdbook-linkcheck
	# Opt-in for checking links in translations - add the language below.
	if: contains(fromJSON('["en", ]'), matrix.language)
	run: cargo install mdbook-linkcheck --locked --version 0.7.7

The problem is likely due to caching: while we only store the cache when building the English version, we use the cache for all languages.

[mgeisler]

@jond01, would you be able to take a look at this?

I think we could clear the mdbook-linkcheck configuration in the book.toml file when we detect that we don't want to run the tool. We could perhaps also just delete the tool preemptively if we see it — since we only store the cache for English, this should work okay.

[jond01]

Hi, sure. It's strange that it happened only now, I will check the caching issue as you suggest.
Attaching a failed run for reference:
https://github.com/google/comprehensive-rust/actions/runs/10055807495/job/27793284713