[#294] Update xrefcheck usage

Description

Problem: we are using a very old version of xrefcheck and call it crossref-verifier even though it was renamed long ago. We would like to keep our version more or less up-to-date.

Solution: use version from Hackage and call it xrefcheck (that's how it is called there).

Related issue(s)

Resolves #294 (closed)

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