Upgrade to Node18 leads to different .map files in 39/311 branches

This may be a regression of MDL-75012, affecting to the 39 and 311 branches.

Was working in an issue about to update libs to moodle-plugin-ci (link), when I saw that the grunt self-test was suddenly failing in all branches.

So I updated the the .js.map file to the new one, because it was expected that, with Node18 and all the changed dependencies, generated files were going to be different.

So far, all ok.

But... once I moved to the new js.map file... 400, 401 and master passed as expected, but 39 and 311 have continued failing, see:

https://github.com/stronk7/moodle-plugin-ci/actions/runs/4331769370

(please, ignore 38_STABLE passing)

So, at the end, I've needed to change this, in order to ignore the 38/39/311 results of the grunt self-test. Because all them are different from the 400/401/master ones.

Talking with dobedobedoh, it seems that he may have found the cause and ALL the branches (39/311/400/401/master) should lead to the same .map files.

So this issue is about to try to fix that. Ciao