CLI: `-u=root` is parsed as `-u root`

[japaric]

trafficstars

relevant test

https://github.com/memorysafety/sudo-rs/blob/ba0ba119ef1a5f2a83cb2e14aae3626b12facbed/test-framework/sudo-compliance-tests/src/cli.rs#L75-L92

this diverges from the original sudo which parses sudo -u=root true as sudo -u =root true

however, both sudo implementations parse sudo -uroot true as sudo -u root true