Bad url link on `dotty.epfl.ch/index.html`

[iusildra]

Compiler version

Nightly build

Minimized code

There is a extra _doc/ in the url of Contributing link

Output

Nothing when clicking on the link

Expectation

Should throw an error, and redirect to https://dotty.epfl.ch/docs/contributing/index.html

[nicolasstucki]

Duplicate of #18285