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/image_test.go

@@ -22,6 +22,13 @@ package main
 import "testing"
 
 func TestImageScanning(t *testing.T) {
+	namespace := allocateNamespace("tis")
+	del, err := setupTestNamespace(namespace)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(del)
+
 	cases := []struct {
 		args       string
 		goldenFile string
@@ -48,13 +55,6 @@ func TestImageScanning(t *testing.T) {
 		},
 	}
 
-	namespace := allocateNamespace("tis")
-	del, err := setupTestNamespace(namespace)
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer del()
-
 	for _, tc := range cases {
 		cmd := cmdTestCase{
 			args:   tc.args + " -n=" + namespace,