GNOME-Software should not say the package is proprietary.

GNOME-Software will say the package is proprietary.
Actually it's MIT-licensed, which qualifies as free software.

This confuses users, and might discourage some users from adopting powershell.

The reason for this is the license field of the official RPM says "MIT License".
It should be "MIT" instead, which is a valid SPDX License Identifier ("MIT License" is not).