fix(healthcheck/reposize): output format

pkg/healthcheck/reposize.go

@@ -34,7 +34,7 @@ func RepoSize(conf_size float64) error {
 		}
 	}
 	if sum > int(conf_size*1024) {
-		return fmt.Errorf("Repository larger than %f M. Please clean up or contact the teaching team.", conf_size)
+		return fmt.Errorf("Repository larger than %.1f Mib. Please clean up or contact the teaching team.", conf_size)
 	}
 	return nil
 }