Add parser tests

[JeroenDeDauw]

AC: we have a passing parser test that tests our lua integration

This parser test will need to create a Module:Whatever page in its setup and then invoke that lua module.

The test could use the real SPARQL endpoint, in which case it's fine if it only works locally, and is skipped on GitHub Actions. OR, the SPARQL request can be intercepted by a test double, since that part is already tested via #4. We do not have a good example of such mocking available and also ran into this challenge at ProfessionalWiki/ExternalContent#52. We'd need to override some MediaWiki services, presumably via the MediaWikiServices class, and only do so during tests. The ParserTestGlobals hook might be a good place to do so (see also https://github.com/ProfessionalWiki/ExternalContent/blob/master/src/EntryPoints/MediaWikiHooks.php#L54).