15.11: Fix loading Web IDE Beta outside gitlab_url

What does this MR do and why?

This backports Fix loading Web IDE Beta outside gitlab_url (!118875 - merged). In %15.11 we enabled the vscode_web_ide by default which caused a regression for some GitLab instances whose gon.gitlab_url doesn't match the actual URL. See originating discussion.

MR acceptance checklist

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• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The original MR has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
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• Ensure the e2e:package-and-test-ee job has either succeeded or been approved by a Software Engineer in Test.

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