message: Remove mention of unsupported '&mut self' for in a query group panic
diff: @@ -87,7 +87,7 @@ pub(crate) fn query_group(args: TokenStream, input: TokenStream) -> TokenStream
  match iter.next() {
  Some(FnArg::SelfRef(sr)) if sr.mutability.is_none() => (),
  _ => panic!(
  - "first argument of query `{}` must be `&self` or `&mut self`",
  + "first argument of query `{}` must be `&self`",
  method.sig.ident
  ),
  }
  