Fix test

Author: bjorn3

src/test/ui/consts/miri_unleashed/mutable_const2.stderr

@@ -10,7 +10,7 @@ error: internal compiler error: mutable allocation in constant
 LL | const MUTABLE_BEHIND_RAW: *mut i32 = &UnsafeCell::new(42) as *const _ as *mut _;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:357:17
+thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:355:17
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 
 error: internal compiler error: unexpected panic