fix(data_source_github_rest_api): only allow for 404 on err

[riezebosch]

Resolves #2156

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Before the change?

• all exceptions are swallowed, even the json decode issue

After the change?

• 404 is allowed as status code (keeping current behaviour), other errors are raised

Pull request checklist

• [x] Tests for the changes have been added (for bug fixes / features)
• [x] 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
• [x] No

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[riezebosch]

Came up with a test by using an endpoint that exceeds the maximum limit for url length.