Register .luacheckrc as a Lua filename

[Alhadis]

Description

This PR adds support for .luacheckrc files.

Checklist:

• I am associating a language with a new filename.
  • The new filename is used in hundreds of repositories:
    • Total results: 2,502 (2,156 sampled)
    • Repositories: 1,801
    • Users: 1,039
  • I have included a real-world usage sample:
    • Source: wow-rp-addons/LibRPMedia
    • License: Public Domain

[stale]

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