Add pdm.lock to TOML and mark as generated

[ghost]

This pull request adds support for recognizing the lock file of PDM, a Python package manager.

Checklist:

• I am associating a language with a new file extension.
  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?l=&q=filename%3Apdm.lock&type=code
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s): generated myself with pdm add requests pyyaml to match the Pipfile
    • Sample license(s): CC0 I guess, not claiming any copyright on it if a machine-generated lock file is even copyrightable
  • I have included a change to the heuristics to distinguish my language from others using the same extension. not applicable since this is a full filename, no known clashes
• I am adding new or changing current functionality
  • I have added or updated the tests for the new or changed functionality.

[lildude]

You've used the wrong section of the template. Please update the OP and fill in the "I am associating a language with a new file extension." section. We especially need to know where the samples come from and the license of each for legal reasons.

[ghost]

Fair enough, I thought this was fine because of this comment:

  <!-- This includes modifying the vendor, documentation, and generated lists. -->

but I guess my PR is kinda a two in one.

I've updated the OP, let me know if it's preferable to take a pdm.lock from an existing project instead of self-generated.

[lildude]

I've updated the OP, let me know if it's preferable to take a pdm.lock from an existing project instead of self-generated.

Perfect 👌

The only thing to do now is sort out the order so the tests pass.