Pin matrix-rageshake to 1.9.0

Related to:

- https://github.com/matrix-org/rageshake/issues/69
- https://github.com/matrix-org/rageshake/pull/70

roles/custom/matrix-rageshake/defaults/main.yml

@@ -16,7 +16,7 @@ matrix_rageshake_path_prefix: /
 
 # There are no stable container image tags yet.
 # See: https://github.com/matrix-org/rageshake/issues/69
-matrix_rageshake_version: "master"
+matrix_rageshake_version: 1.9.0
 
 matrix_rageshake_base_path: "{{ matrix_base_data_path }}/rageshake"
 matrix_rageshake_config_path: "{{ matrix_rageshake_base_path }}/config"