This silences a very noisy deprecation warning from rustc:

    warning: trailing semicolon in macro used in expression position
       --> src/webcore/macros.rs:179:141
        |
    179 |   ... [$($arg_names)* $arg_name] [$($unused_arg_names)*] -> $($rest)* );
        |                                                                        ^
        |
       ::: src/webapi/form_data.rs:144:9
        |
    144 | /         js! (
    145 | |             return @{self}.has(@{name});
    146 | |         ).try_into().unwrap()
        | |_________- in this macro invocation
        |
        = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
        = note: for more information, see issue #79813 <rust-lang/rust#79813>
        = note: this warning originates in the macro `$crate::_js_impl` (in Nightly builds, run with -Z macro-backtrace for more info)