tests: only provide template values when used

As otherwise the `.golden` values can not be automatically updated using
`-update` as documented in `CONTRIBUTING.md`.

Also ensure we do not use `defer` but rather `t.Cleanup` in tests, as
this will always be called even if e.g. `t.Fatal` absruptly stops the
test.

Signed-off-by: Hidde Beydals <hello@hidde.co>

cmd/flux/install_test.go

@@ -25,9 +25,7 @@ func TestInstall(t *testing.T) {
 	// Given that this test uses an invalid namespace, it ensures
 	// to restore whatever value it had previously.
 	currentNamespace := *kubeconfigArgs.Namespace
-	defer func() {
-		*kubeconfigArgs.Namespace = currentNamespace
-	}()
+	t.Cleanup(func() { *kubeconfigArgs.Namespace = currentNamespace })
 
 	tests := []struct {
 		name   string