twig regexp need double slash escaping

templates/admin/core_custom/custom-fields/element-data.html.twig

@@ -14,7 +14,7 @@
             {% set readonly = true %}
             {% set value = value|json_encode %}
           {% endif %}
-          {% if key matches '/^osm\//' %}
+          {% if key matches '/^osm\\//' %}
             {% set readonly = true %}
           {% endif %}
           <input type="{{ type }}" class="form-control" {{ readonly ? 'readonly="readonly"' : '' }}