Rollup merge of #137120 - ChrisDenton:its-all-relative, r=GuillaumeGomez

Enable `relative-path-include-bytes-132203` rustdoc-ui test on Windows

The problem with the error message on Windows is:

- The path separators are different
- The OS error message string is different

Normalizing those two things makes the test pass on Windows.

Author: matthiaskrgr