E0275: Point a additional error case while waiting for a proper fix

[louwenus]

Dirty fix to #145069
While waiting for a proper fix, at least document what is happening in the error so that the next to stumble on the issue hopefully does not waste too much time debugging it.

[rustbot]

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[rustbot]

⚠️ Warning ⚠️

• There are issue links (such as #123) in the commit messages of the following commits.
  Please move them to the PR description, to avoid spamming the issues with references to the commit, and so this bot can automatically canonicalize them to avoid issues with subtree.
  • 9c55d56

[louwenus]

⚠️ Warning ⚠️

* There are issue links (such as `#123`) in the commit messages of the following commits.
  _Please move them to the PR description, to avoid spamming the issues with references to the commit, and so this bot can automatically canonicalize them to avoid issues with subtree._
  
  * [9c55d56](https://github.com/rust-lang/rust/commit/9c55d5676bcb74b23934b7b4f3147cab4083a889)

Well it is in the PR description too, and I do not know how to edit commit message.
If it is important, could someone tell me how to do it ? Thanks