Easier reproducer:
>>> import gc
>>> gc.get_referrers(x)
AddressSanitizer:DEADLYSIGNAL
=================================================================
==17017==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x000000000000 bp 0x7fff93f8f7a0 sp 0x7fff93f8f758 T0)
==17017==Hint: pc points to the zero page.
==17017==The signal is caused by a READ memory access.
==17017==Hint: address points to the zero page.
#0 0x0 (<unknown module>)
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (<unknown module>)
==17017==ABORTING