Correctly use subtests in helm template tests

The testing.T in the subtest wasn't being used, so subtests were
effectively not being used. Additionally, in case subtests run in
parallel, we assign tt := tt to fix closure captures on range variables,
since the variables produced by a range are re-used between iterations.

cmd/helm/template_test.go

@@ -132,7 +132,8 @@ func TestTemplateCmd(t *testing.T) {
 
 	var buf bytes.Buffer
 	for _, tt := range tests {
-		t.Run(tt.name, func(T *testing.T) {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
 			// capture stdout
 			old := os.Stdout
 			r, w, _ := os.Pipe()