Add requirements.lock.txt as Pip Requirements filename

[starwarswii]

Adds requirements.lock.txt as a filename for the Pip Requirements language

Description

Checklist:

• I am adding a new extension to a language.
  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3Arequirements.lock.txt
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • https://github.com/AcTePuKc/Chatterbox-TTS-UI/blob/72da14c3b0df2124c2ca49d3d65f0b6b855c4791/requirements.lock.txt
    • Sample license(s):
      • MIT License
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

[lildude]

LGTM. Thanks.

Important

The changes in this PR will not appear on GitHub until the next release has been made and deployed. See here for more details.