compiler-rt/test/fuzzer/fork.test is flaky on sanitizer-x86_64-linux-fuzzer

[MaskRay]

Its failure rate in the past few days is quite high. https://lab.llvm.org/buildbot/#/builders/75 Example failure message:

+ : 'RUN: at line 17'
+ FileCheck /b/sanitizer-x86_64-linux-fuzzer/build/llvm-project/compiler-rt/test/fuzzer/fork.test --check-prefix=CRASH
+ not /b/sanitizer-x86_64-linux-fuzzer/build/llvm_build0/runtimes/runtimes-bins/compiler-rt/test/fuzzer/X86_64LibcxxLinuxConfig/Output/fork.test.tmp-ShallowOOMDeepCrash -fork=1 -rss_limit_mb=128
/b/sanitizer-x86_64-linux-fuzzer/build/llvm-project/compiler-rt/test/fuzzer/fork.test:15:8: error: CRASH: expected string not found in input
CRASH: {{SEGV|access-violation}} on unknown address 0x00000000
       ^
<stdin>:1:1: note: scanning from here
INFO: Running with entropic power schedule (0xFF, 100).
^
<stdin>:25:157: note: possible intended match here
Live Heap Allocations: 24204998 bytes in 79 chunks; quarantined: 41374468 bytes in 62041 chunks; 127070 other chunks; total chunks: 189190; showing top 95% (at most 8 unique contexts)
                                                                                                                                                            ^

Input file: <stdin>
Check file: /b/sanitizer-x86_64-linux-fuzzer/build/llvm-project/compiler-rt/test/fuzzer/fork.test

The test hasn't been changed since Dec 2022. There are very few changes to compiler-rt/lib/fuzzer in the last month.