refactor(git): commitDate explicitly set default for refDate

[xDivisionByZerox]

The default value of the refDate option in faker.git.commitDate() is documented as now (new Date()).
This only happens due to the underlying implementation in faker.date.recent().
If the default value in recent() should change in the future, this change ensures that commitDate() still works the same.

[xDivisionByZerox]

I'm not sure if this should be labeled as chore, since it doesn't really change anything at runtime currently.

[codecov]

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Additional details and impacted files

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[ST-DDT]

There seems to be a merge conflict. Could you please fix it?