formatting of error code

Author: marten-seemann

content/docs/http3/server.md

@@ -126,7 +126,7 @@ defer cancel()
 server.Shutdown(ctx)
 ```
 
-On the wire, graceful shutdown is signaled by sending a GOAWAY frame. This tells clients that the server will not accept any new requests. Requests received after sending the GOAWAY frame are rejected (using the H3_REQUEST_REJECTED error code). Existing connections are not closed; clients are expected to close them after they finish processing their requests.
+On the wire, graceful shutdown is signaled by sending a GOAWAY frame. This tells clients that the server will not accept any new requests. Requests received after sending the GOAWAY frame are rejected (using the `H3_REQUEST_REJECTED` error code). Existing connections are not closed; clients are expected to close them after they finish processing their requests.
 
 `Shutdown` returns when all existing connections have been closed, or when the context is canceled. In that case, all remaining active QUIC connections are closed, which abruptly terminates the remaining requests.