Wrong locale name in unit test file

[matsduf]

In t/usage.t in develop branch a locale name has the wrong format. It reads as sv_SE.utf8, but it should be sv_SE.UTF-8, the general name of the locale.

        skip 'sv_SE.utf8 locale is unavailable', 5
          if !has_locale( 'sv_SE.utf8' );

        check_success '--json-stream --no-raw',
          [ '--test=basic01', '--json-stream', '--no-raw', '--locale=sv_SE.utf8', '--level=INFO', '.' ], sub {

https://github.com/zonemaster/zonemaster-cli/blob/develop/t/usage.t#L299-L303

There are more instances in the file.