docs: fix erroneous github_repository_file docs

[GilUpstream]

• Updates the docs with the correct default set for the branch argument

Resolves #1539

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Behavior

Before the change?

• Docs lead provider consumers to believe the default branch will be using when using the data source without a branch argument.

After the change?

• Consumers of this provider will know that main will be used as the branch if it is not supplied.

Other information

• Removed the note about the branch already existing as well since that is relevant to the resource for github_repository_file only.

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Additional info

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)
• Added the appropriate label for the given change

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes (Please add the Type: Breaking change label)
• No

If Yes, what's the impact:

• N/A

Pull request type

Please add the corresponding label for change this PR introduces:

• Bugfix: Type: Bug
• Feature/model/API additions: Type: Feature
• Updates to docs or samples: Type: Documentation
• Dependencies/code cleanup: Type: Maintenance

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[nickfloyd]

@GilUpstream Thanks for the update for clarity here. This does make me wonder if this particular aspect of the provider is working as it should - i.e. It should use the default branch and not just main (which could be different from the default).

@kfcampbell Do you have any thoughts or feels on this specific behavior?

[kfcampbell]

Agreed that we should look up the default branch; I've created #1546 to track that work. In the meantime, this PR is an improvement in that the docs will match the behavior.

[GilUpstream]

@GilUpstream Thanks for the update for clarity here. This does make me wonder if this particular aspect of the provider is working as it should - i.e. It should use the default branch and not just main (which could be different from the default).

@kfcampbell Do you have any thoughts or feels on this specific behavior?

Agreed! I'm currently using the github_repository data source to look up the repo's default branch. My configs would be much simpler if the default branch was used.