Fix unterminated placeholder in a matrix-synapse deprecation message

The `matrix_synapse_experimental_features_msc3202_device_masquerading_enabled`
entry was missing its closing angle bracket, so anyone still setting
that variable was told to rename it to `<removed - this feature is
enabled by default now`.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

roles/custom/matrix-synapse/tasks/validate_config.yml

@@ -74,7 +74,7 @@
     - {'old': 'matrix_synapse_rust_synapse_compress_state_docker_image_registry_prefix_upstream', 'new': 'matrix_synapse_rust_synapse_compress_state_container_image_registry_prefix_upstream'}
     - {'old': 'matrix_synapse_rust_synapse_compress_state_docker_image_registry_prefix_upstream_default', 'new': 'matrix_synapse_rust_synapse_compress_state_container_image_registry_prefix_upstream_default'}
 
-    - {'old': 'matrix_synapse_experimental_features_msc3202_device_masquerading_enabled', 'new': '<removed - this feature is enabled by default now'}
+    - {'old': 'matrix_synapse_experimental_features_msc3202_device_masquerading_enabled', 'new': '<removed - this feature is enabled by default now>'}
 
     - {'old': 'matrix_synapse_experimental_features_msc3861_enabled', 'new': 'matrix_synapse_matrix_authentication_service_enabled'}
     - {'old': 'matrix_synapse_experimental_features_msc3861_issuer', 'new': '<superseded by matrix_synapse_matrix_authentication_service_endpoint>'}