Make docs test CI always run, even for cases where nothing inside /docs folder was touched

[novusnota]

That's because the Cookbook checks now depend on the repo version of the compiler and not on the one installed in npm.

Therefore, some code samples might start breaking all of a sudden, so it's better to always run docs CI, especially considering that it takes no more than 2 minutes, usually less.

The problem was discovered in #2529, but introduced in another PR, which didn't touch anything inside docs.