Rollup merge of #139822 - 0x79de:fix-eopnotsupp-mapping, r=dtolnay

Fix: Map EOPNOTSUPP to ErrorKind::Unsupported on Unix

This change maps the EOPNOTSUPP errno value (95) to std::io::ErrorKind::Unsupported in the decode_error_kind function for Unix platforms. Previously, it was incorrectly mapped to ErrorKind::Uncategorized.

Fixes #139803

Author: Zalathar