Recently introduced assertion is too strong:
```
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/codebuild/output/src2096/src/s3/00/src/hotspot/share/gc/shenandoah/shenandoahReferenceProcessor.cpp:332), pid=1373, tid=1375
# Error: Marking should be complete for object 0x00000007ffc029b0 in the Old generation
```