Enhance GithHub publishing logic to handle renamed repositories

[nomike]

Fixes #245022.

Steps to test the fix

1. Sign up for GitHub
2. Create repository "test" on GitHub
3. Rename that repository to "test-renamed"
4. Login to your GitHub account from within vscode
5. Initialize a new git repository in vscode and commit a test file
6. Chose the "Publish to GitHub" command
7. Use "test" as a repository name

With the current version, vscode will complain that the repository already exists, even though it no longer does.
My MR fixes this, publishing is now possible again.

Testing

I don't thing it's feasible to write a unit test for this, as that would require a GitHub account and a repository which needs to be created and deleted on each test run.