Apply GitHub server flag when resolving factory URL

[vinokurig]

What does this PR do?

Fix an issue when starting a workspace using a public GitHub Server repo fails.

Screenshot/screencast of this PR

What issues does this PR fix or reference?

https://issues.redhat.com/browse/CRW-6831

How to test this PR?

Start a workspace from a public GitHub Enterprise Server repository with a devfile. See: workspace starts

PR Checklist

As the author of this Pull Request I made sure that:

• [ ] The Eclipse Contributor Agreement is valid
• [ ] Code produced is complete
• [ ] Code builds without errors
• [ ] Tests are covering the bugfix
• [ ] The repository devfile is up to date and works
• [ ] Sections What issues does this PR fix or reference and How to test this PR completed
• [ ] Relevant user documentation updated
• [ ] Relevant contributing documentation updated
• [ ] CI/CD changes implemented, documented and communicated

Reviewers

Reviewers, please comment how you tested the PR when approving it.