Gitpod: `Copy GitHub link` is broken in diff editors.

[kittaakos]

Describe the bug

Steps to reproduce

Copy GitHub link is broken in diff editors.

• Open Gitpod on this PR: https://github.com/eclipse-theia/theia/pull/7159
• In the sidepanel.css (4d4f6c293907893670c7aa7c11b55c4811d004a3) ⟷ sidepanel.css diff editor right-click in line 85 and select Copy GitHub link.
• I have this URL: https://github.com/Anasshahidd21/theia/tree/dc16e5841d5a34766e19cdba597b7c5252cbb351#L85. It does not seem good, and it does not open the file if I paste it in the browser.

Remarks:

• It works in code editors.

Expected behavior

Additional Information

Example Repository

[jankeromnes]

Funny enough, https://github.com/gitpod-io/gitpod/issues/322 was filed exactly 1 year ago, on February 19th! 😂 🎂

In honor of this, I think we should fix it.