checker: do not allow arr1=arr2 without cloning

cmd/tools/modules/testing/common.v

@@ -296,7 +296,7 @@ pub fn prepare_test_session(zargs string, folder string, oskipped []string, main
 	mut session := new_test_session(vargs)
 	files := os.walk_ext(os.join_path(parent_dir, folder), '.v')
 	mut mains := []string{}
-	mut skipped := oskipped
+	mut skipped := oskipped.clone()
 	for f in files {
 		if !f.contains('modules') && !f.contains('preludes') {
 			// $if !linux {

cmd/tools/vtest-fixed.v

@@ -42,7 +42,7 @@ fn main() {
 	vexe := pref.vexe_path()
 	vroot := os.dir(vexe)
 	os.chdir(vroot)
-	args := os.args
+	args := os.args.clone()
 	args_string := args[1..].join(' ')
 	cmd_prefix := args_string.all_before('test-fixed')
 	title := 'testing all fixed tests'