fix: update test to expect null connection_id when not set

After removing the default of 0 from connection_id, the API value
of 0 is now treated as null in state. Update the assertion accordingly.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: trouze

pkg/framework/objects/environment/resource_acceptance_test.go

@@ -70,10 +70,9 @@ func getBasicConfigWithModifiedConfigTestStep(projectName, environmentName, cust
 				"deployment_type",
 				"production",
 			),
-			resource.TestCheckResourceAttr(
+			resource.TestCheckNoResourceAttr(
 				"dbtcloud_environment.test_env",
 				"connection_id",
-				"0",
 			),
 		),
 	}