Mark `deno.lock` as generated

[lishaduck]

Mark deno.lock files as generated by the deno cli.

Closes: #6882

Description

Checklist:

• [x] I am adding new or changing current functionality
  • [ ] I have added or updated the tests for the new or changed functionality.

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I'm not sure where to place a deno.lock for tests. I greped around, but I couldn't find a Dummy/ folder.

[lildude]

I'm not sure where to place a deno.lock for tests. I greped around, but I couldn't find a Dummy/ folder.

We already have one: https://github.com/github-linguist/linguist/blob/master/samples/JSON/filenames/deno.lock

https://github.com/github-linguist/linguist/pull/6783 is a recent PR you can copy.