Sweeper should not CompiledIC::set_to_clean with ICStubs for is_unloading() nmethods

The following test is failing the JDK14 CI:

applications/runthese/RunThese24H.java

Here's a snippet from the hs_err_pid file:

# Internal Error (open/src/hotspot/share/gc/z/zVerify.cpp:43), pid=7849, tid=7882
# guarantee(ZAddress::is_good(addr)) failed: Bad oop 0x00001075670c1418 found at 0x00007fb7ed656418
#
# JRE version: Java(TM) SE Runtime Environment (14.0+24) (fastdebug build 14-ea+24-1081)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 14-ea+24-1081, mixed mode, tiered, z gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x181ae30] verify_oop(oop*)+0xa0

--------------- T H R E A D ---------------

Current thread (0x00007fb8042d6030): VMThread "VM Thread" [stack: 0x00007fb8084a8000,0x00007fb8085a8000] [id=7882]

Stack: [0x00007fb8084a8000,0x00007fb8085a8000], sp=0x00007fb8085a64a0, free space=1017k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x181ae30] verify_oop(oop*)+0xa0
V [libjvm.so+0x132699b] nmethod::oops_do(OopClosure*, bool)+0x2bb
V [libjvm.so+0xd7831e] CodeBlobToOopClosure::do_code_blob(CodeBlob*)+0x2e
V [libjvm.so+0x180776b] ZRootsIteratorCodeBlobClosure::do_code_blob(CodeBlob*)+0x3b
V [libjvm.so+0x18077dd] ZRootsIteratorThreadClosure::do_thread(Thread*)+0x5d
V [libjvm.so+0x1672cd9] Threads::possibly_parallel_threads_do(bool, ThreadClosure*)+0x169
V [libjvm.so+0x1805588] ZRootsIterator::oops_do(ZRootsIteratorClosure*)+0x1f8
V [libjvm.so+0x181b6ad] ZVerify::before_zoperation()+0x10d
V [libjvm.so+0x17cbf66] VM_ZOperation::doit()+0x46
V [libjvm.so+0x172c983] VM_Operation::evaluate()+0x143
V [libjvm.so+0x175b4b8] VMThread::evaluate_operation(VM_Operation*) [clone .constprop.66]+0x2b8
V [libjvm.so+0x175bf8e] VMThread::loop()+0x91e
V [libjvm.so+0x175c22a] VMThread::run()+0xca
V [libjvm.so+0x16759d6] Thread::call_run()+0xf6
V [libjvm.so+0x13a7b9e] thread_native_entry(Thread*)+0x10e


Starting this as a confidential bug since this is a closed test.
Update: Leonid said the failure sighting can be non-confidential.