pre-commit: move target directory from entry to args

[GideonBear]

PR Checklist

• A description of the changes is added to the description of this PR.
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• If you've fixed a bug or added code that should be tested, add tests!
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Description of changes

Ref #840

Previously, running deptry in pre-commit when using a src directory:

• with no args, results in DEP003 'mypackage' imported but it is a transitive dependency
• with args: [ src ], results in double reports
• with entry: deptry src, provides the correct behavior

However, entry is supposed to be an internal implementation detail, while args is meant for users to override. In this PR I've moved the directory to args so it can be overridden by args: [ "src" ] instead.

This is a breaking change, since anyone using args: [ "--something" ] will now be running deptry --something instead of deptry . --something, and need to edit their config to args: [ ".", "--something" ]. So feel free to deny if this isn't important enough to warrant that.