Use placeholder credentials in registry resolution tests

Agent-Logs-Url: https://github.com/j143/basic-docker-engine/sessions/9b259d2d-2dd2-4094-849b-5fb1f50355c2

Co-authored-by: j143 <53068787+j143@users.noreply.github.com>

Author: Copilot

main_test.go

@@ -160,13 +160,13 @@ func TestResolveRegistry(t *testing.T) {
 		},
 		{
 			name:           "credentialed local registry over http",
-			imageName:      "user:password@localhost:5000/alpine",
+			imageName:      "testuser:testpass@localhost:5000/alpine",
 			wantRegistry:   "http://localhost:5000/v2/",
 			wantRepository: "alpine",
 		},
 		{
 			name:           "credentialed local registry with @ in username over http",
-			imageName:      "user@domain:password@localhost:5000/alpine:latest",
+			imageName:      "testuser@example.com:testpass@localhost:5000/alpine:latest",
 			wantRegistry:   "http://localhost:5000/v2/",
 			wantRepository: "alpine:latest",
 		},