assert(!m->is_old() || ik()->is_being_redefined()) failed: old methods should not be in vtable

# Symptom

```
IsModifiableClassAgent started
# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=/klassVtable.cpp:564
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/root/df/jdk/src/hotspot/share/oops/klassVtable.cpp:564), pid=10502, tid=10505
# assert(!m->is_old() || ik()->is_being_redefined()) failed: old methods should not be in vtable
#
# JRE version: OpenJDK Runtime Environment TencentKonaJDK (16.0+4) (fastdebug build 16-internal+4-adhoc.root.jdk)
# Java VM: OpenJDK 64-Bit Server VM TencentKonaJDK (fastdebug 16-internal+4-adhoc.root.jdk, mixed mode, sharing, tiered, compressed oops, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x10fdc84] klassVtable::put_method_at(Method*, int)+0x2e4
```

# Reproduce

jtreg run: java/lang/instrument/IsModifiableClassAgent.java