The core dump in https://spruce.mongodb.com/task/mongodb_mongo_master_linux_arm64_tsan_essential_required_unit_tests_patch_8db80b988938fd62aa30edeae819c72c7a3f2143_69723dfe6eb07700073063d1_26_01_22_15_11_23/files?execution=0&sorts=STATUS%3AASC is a core dump of a bash process, not the unit test.

It's backtrace is:

#0 0x0000ffffafec6e98 in wait4 ()
  from /home/ec2-user/rbe_sysroot/lib64/libc.so.6
#1 0x0000aaaad6be8dc4 [PAC] in waitchld.constprop ()
#2 0x0000aaaad6b47694 [PAC] in wait_for ()
#3 0x0000aaaad6b31388 [PAC] in execute_command_internal ()
#4 0x0000aaaad6b8fee8 [PAC] in parse_and_execute ()
#5 0x0000aaaad6b90cdc [PAC] in evalstring ()
#6 0x0000aaaad6b2ab14 [PAC] in execute_builtin ()
#7 0x0000aaaad6b2c66c [PAC] in execute_subshell_builtin_or_function ()
#8 0x0000aaaad6b2cda4 [PAC] in execute_simple_command ()
#9 0x0000aaaad6b2e9e8 [PAC] in execute_command_internal ()
#10 0x0000aaaad6b2fe1c [PAC] in execute_command_internal ()
#11 0x0000aaaad6b314a0 [PAC] in execute_command ()
#12 0x0000aaaad6b1c954 [PAC] in reader_loop ()
#13 0x0000aaaad6b11b80 [PAC] in main ()

I suspect that the following is not a robust enough mechanism to capture the child test process: https://github.com/10gen/mongo/blob/92c7a2535b06223738fffe65ea817cc8049f5925/bazel/test_wrapper.sh#L23