Follow up to https://github.com/ziglang/zig/pull/17069.

This TODO being left in was a complete oversight.

Before, any 'retryable' error would hit:

error: thread 2920 panic: access of union field 'success' while field 'failure_retryable' is active

Now, it will be reported/handled properly:

C:\Users\Ryan\Programming\Zig\zig\test\standalone\windows_resources\res\zig.rc:1:1: error: FileNotFound