[naga test] Add #[track_caller] to wgsl_errors::check.

Add a `#[track_caller]` attribute to the `check` function in
`wgsl_errors`, so that test failures point to the actual test case,
not to the helper function.

Author: jimblandy

naga/tests/wgsl_errors.rs

@@ -5,6 +5,7 @@ Tests for the WGSL front end.
 
 use naga::valid::Capabilities;
 
+#[track_caller]
 fn check(input: &str, snapshot: &str) {
     let output = naga::front::wgsl::parse_str(input)
         .expect_err("expected parser error")