ci: reduce repetitions in test_global_mutex in init_global_test.v

With the old number of repetitions (2500000), that test alone could take over
30 seconds, in the CI environment.

vlib/v/tests/init_global_test.v

@@ -168,7 +168,7 @@ fn switch2() u64 {
 fn test_global_mutex() {
 	assert f1 == 34.0625
 	t := go switch2()
-	for _ in 0 .. 2500000 {
+	for _ in 0 .. 25000 {
 		mtx.@lock()
 		f1, f2 = f2, f1
 		mtx.unlock()