internal/rosa/python: run tests via helper

Despite the lack of standards, pytest seems somewhat widely agreed upon.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/meson.go

@@ -22,7 +22,7 @@ func (t Toolchain) newMeson() (pkg.Artifact, string) {
 		},
 	}, &PipHelper{
 		EnterSource: true,
-		Script: `
+		Check: `
 cd 'test cases'
 rm -rf \
 	'common/32 has header' \