Trailing whitespace in errors

[wooster0]

While working on #89963 I had some issues with my editor automatically trimming trailing whitespace on save when I edited .stderr files so I had to disable that. I don't think any errors should contain trailing whitespace in the first place though. If you search the codebase with regex ^ \| $ you will find tons of such cases.

I have the slight feeling that whitespace might just originate from only a single location somewhere in the error printing code so perhaps this is an easy fix and thus probably worth fixing.
A pattern I noticed is that the trailing whitespace pretty much always seems to come at the end of a help: suggestion.

To be fair there's far more whitespace though. If you put src/**/*.stderr in files to include and use \s$ as the regex, you will find even more.

[nagisa]

You can use ./x.py test --bless to update the test files, rather than editing them manually.