catch unwind in parallel mode during wfcheck
Update #75760
When performing wfcheck, from the test results, the parallel mode will stop all checks when an `item`'s check failed, (e.g. the first ui test failure raised from [here](https://github.com/rust-lang/rust/blob/master/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs#L249))while the serial mode will output each `item`'s check result via `catch_unwind`. This leads to inconsistencies in the final output of the two mode.
In my local environment, this modification prevents the following ui tests from failing when set `parallel-compiler = true` in `config.toml`:
```
[ui] src/test\ui\associated-types\defaults-cyclic-fail-1.rs
[ui] src/test\ui\associated-types\defaults-cyclic-fail-2.rs
[ui] src/test\ui\associated-types\hr-associated-type-bound-2.rs
[ui] src/test\ui\associated-types\impl-wf-cycle-1.rs
[ui] src/test\ui\associated-types\impl-wf-cycle-2.rs
[ui] src/test\ui\issues\issue-20413.rs
[ui] src/test\ui\parallel_test\defaults-cyclic-fail-para.rs
```
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