fix: TestResetFlagToDefault uses NewTestKit per cmd test harness convention

CodeRabbit follow-up on PR #3022: this test builds its own local
pflag.FlagSet rather than touching RootCmd, but cmd package tests must
still call NewTestKit(t) per repo convention, for consistency and to guard
against future edits that do touch global state.

Author: osterman

cmd/testkit_test.go

@@ -327,6 +327,8 @@ func TestTestKit_RestoresAtmosConfig(t *testing.T) {
 // --version flag's DefValue to "" for cleaner help output, and pflag's bool
 // Set("") fails, so a naive Set(DefValue) would leave a leaked true in place.
 func TestResetFlagToDefault(t *testing.T) {
+	_ = NewTestKit(t)
+
 	fs := pflag.NewFlagSet("test", pflag.ContinueOnError)
 	fs.Bool("version", false, "")
 	fs.String("stack", "", "")