benchmark: allow range trailing comma in RangeArgs (#3598)

Rustfmt will add a trailing comma for longer expression, this change
will make sure that the Range parameters can still be parsed.

---------

Co-authored-by: command-bot <>
Co-authored-by: Alexander Theißen <alex.theissen@me.com>

substrate/frame/support/procedural/src/benchmark.rs

@@ -65,6 +65,7 @@ struct RangeArgs {
 	start: syn::GenericArgument,
 	_comma: Comma,
 	end: syn::GenericArgument,
+	_trailing_comma: Option<Comma>,
 	_gt_token: Gt,
 }