Accept venues with mul label too

[egonw]

Fixes the problem that BioHackrXiv preprints are not showing up:

Description

Because venues can have their label as mul too now, filtering on LANG() = 'en' should now also include allow it to have the value mul.

This probably applies to more SPARQL queries.

Caveats

Check any of the following which apply:

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
  • I have made corresponding changes to the documentation
• This change requires new dependencies (please list)

Testing

Check the "Number of articles with CiTO-annotated citations by year" section at

• https://scholia.toolforge.org/cito/#articles-by-year

Checklist

• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have not used code from external sources without attribution
• I have considered accessibility in my implementation
• There are no remaining debug statements (print, console.log, ...)