Rollup merge of #129154 - wafarm:fix-95463, r=estebank

Fix wrong source location for some incorrect macro definitions

Fixes #95463

Currently the code will consume the next token tree after `var` when trying to parse `$var:some_type` even when it's not a `:` (e.g. a `$` when input is `($foo $bar:tt) => {}`). Additionally it will return the wrong span when it's not a `:`.

This PR fixes these problems.