Update grafana (7.5.6->7.5.7)

roles/matrix-grafana/defaults/main.yml

@@ -3,7 +3,7 @@
 
 matrix_grafana_enabled: false
 
-matrix_grafana_version: 7.5.6
+matrix_grafana_version: 7.5.7
 matrix_grafana_docker_image: "{{ matrix_container_global_registry_prefix }}grafana/grafana:{{ matrix_grafana_version }}"
 matrix_grafana_docker_image_force_pull: "{{ matrix_grafana_docker_image.endswith(':latest') }}"