Spurious tests/ui/panics/default-backtrace-ice.rs failures

[Noratrieb]

---- [ui] tests/ui/panics/default-backtrace-ice.rs stdout ----
diff of stderr:

7 
8 aborting due to `-Z treat-err-as-bug=1`
- (end_short_backtrace)
11 (begin_short_backtrace)
12 (end_short_backtrace)
13 (begin_short_backtrace)
---

The error has been seen on x86_64-apple-2 and on i686-mingw so far.

The test was last touched in #111052, cc @nnethercote

#114465 (comment)
#115645 (comment)
#116548 (comment)
#115927 (comment)
#116530 (comment)
#116527 (comment)
#109882 (comment)
#116915 (comment)

[sthibaul]

Also Cc-ing @chenyukang who added the duplicate end_short_backtrace/begin_short_backtrace