GitHub Action CI: Add Go source file format check (#6090)

https://github.com/XTLS/Xray-core/pull/6057#issuecomment-4364819830

And https://github.com/XTLS/Xray-core/pull/6149#issuecomment-4546876261

common/platform/platform_test.go

@@ -36,9 +36,10 @@ func TestNormalizeEnvName(t *testing.T) {
 }
 
 func TestEnvFlag(t *testing.T) {
-	if v := (EnvFlag{
+	v := EnvFlag{
 		Name: "xxxxx.y",
-	}.GetValueAsInt(10)); v != 10 {
+	}.GetValueAsInt(10)
+	if v != 10 {
 		t.Error("env value: ", v)
 	}
 }