Rename syncing-a-fork.md to syncing-a-fork.md7

[Tonymmm]

Why:

What's being changed:

Check off the following:

• I have reviewed my changes in staging. (look for the deploy-to-heroku link in your pull request, then click View deployment)
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[welcome]

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