Improve coverage of big.c #4637

Job	Run time
Build Erlang/OTP (64-bit)	8m 49s
Event File	4s
Create SBOM	0s
Build Erlang/OTP (iOS)	4m 8s
Build Erlang/OTP (32-bit)	5m 5s
Build Erlang/OTP (cross-compile)	10m 17s
Build Erlang/OTP (Windows)	18m 15s
Build Erlang/OTP (macOS)	3m 41s
Build Erlang/OTP (FreeBSD)	3m 22s
Test Erlang/OTP (debug)	4m 23s
Build Erlang/OTP (Types and Flavors)	10m 51s
Run static analysis	6m 8s
Build Erlang/OTP (clang)	5m 23s
Build and check documentation	4m 48s
Test Erlang/OTP (emulator)	49m 16s
Release Erlang/OTP	0s
Test Erlang/OTP (system)	7m 22s
	2h 21m 52s

Provide feedback