sync: only run channel_select_test.v when VTEST_RUN_FLAKY=1

vlib/sync/channel_select_test.v

@@ -7,8 +7,17 @@ module sync
 // For that, please look at `channel_select_2_test.v` or `channel_select_3_test.v`
 // This test case uses the implementation in `sync/channels.v` directly
 // in order to test it independently from the support in the core language
+import os
 import time
 
+fn test_should_run_flaky_test() {
+	if os.getenv('VTEST_RUN_FLAKY') != '1' {
+		eprintln('> skipping running flaky test, set VTEST_RUN_FLAKY to 1, to run it')
+		exit(0)
+	}
+	assert true
+}
+
 fn do_rec_i64(mut ch Channel) {
 	mut sum := i64(0)
 	for _ in 0 .. 300 {