fix(github_repository_file): Commit detail changes should not do empty commits

[atorrescogollo]

When terraform changes any field related to how commits are done (email, commit message, etc), it pushes an unexpected empty commit to the repo.

This is specially relevant when importing an existing file into terraform, where the commit message you put in terraform will likely be different from the commit that pushed the file originally. In that sense, importing a file will always mean eventually doing empty commits for each file you imported.

The expected behaviour is just updating the state and avoid doing those empty commits. Otherwise, each empty commit can run any CI that might be configured, notifications, etc.

Resolves #689

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Before the change?

• When any of commit_sha, commit_author, commit_email or commit_message changed, it did a empty commit

After the change?

• Now, it checks which fields have changes and only commits if there are changes in any other field

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

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