Fix deprecated trailing semicolons in macros

[notriddle]

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 <https://github.com/rust-lang/rust/issues/79813> = note: this warning originates in the macro `$crate::_js_impl` (in Nightly builds, run with -Z macro-backtrace for more info)