tests: update missing_pin_data error expectation

Update the expected compiler error output for the missing_pin_data UI test
to match the current Rust compiler's actual error message format. The
compiler no longer includes the 'help' suggestion that was previously
part of the error output.

This resolves test failures caused by changes in compiler error message
formatting between Rust versions.

Author: liamjdavis

tests/ui/compile-fail/init/missing_pin_data.stderr

@@ -11,9 +11,3 @@ error[E0599]: no associated item named `__pin_data` found for struct `Foo` in th
   = note: the following trait defines an item `__pin_data`, perhaps you need to implement it:
           candidate #1: `HasPinData`
   = note: this error originates in the macro `$crate::try_pin_init` which comes from the expansion of the macro `pin_init` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: there is an associated function `__init_data` with a similar name
- --> src/lib.rs
-  |
-  -             @has_data(HasPinData, __pin_data),
-  +             @has_data(HasPinData, __init_data),
-  |