Fix incorrectly espaced HTML for redaction reason

A redacted event with a reason containing problematic HTML characters,
e.g. "<test>" would render as literal escaped HTML, e.g. "&lt;test&gt;"

src/backend/matrix_client.py

@@ -1313,7 +1313,7 @@ class MatrixClient(nio.AsyncClient):
                   "%1's message was removed by %2"
 
         if reason:
-            content = f"{content}, reason: {html.escape(reason)}"
+            content = f"{content}, reason: {reason}"
 
         return content