commit-graph: fix topo_levels slab propagation regression #28955

Job	Run time
config	7s
fuzz smoke test	1m 28s
win build	4m 46s
osx-gcc (macos-14)	35m 5s
win+Meson build	4m 16s
osx-meson (macos-14)	1h 1m 1s
sparse	4m 0s
osx-reftable (macos-14)	29m 43s
static-analysis	6m 19s
osx-clang (macos-14)	35m 3s
documentation	7m 38s
rust-analysis	1m 39s
linux-meson (ubuntu:rolling)	24m 31s
linux32 (i386/ubuntu:20.04)	6h 0m 4s
debian-11 (debian:11)	24m 9s
fedora-breaking-changes-meson (fedora:latest)	15m 55s
almalinux-8 (almalinux:8)	25m 10s
linux-reftable (ubuntu:rolling)	16m 46s
linux-TEST-vars (ubuntu:20.04)	28m 6s
linux-reftable-leaks (ubuntu:rolling)	57m 21s
linux-breaking-changes (ubuntu:rolling)	28m 15s
linux-leaks (ubuntu:rolling)	59m 31s
linux-asan-ubsan (ubuntu:rolling)	1h 14m 20s
linux-musl-meson (alpine:latest)	1h 6m 2s
win+VS build	0s
linux-sha256 (ubuntu:rolling)	26m 15s
win+VS test	-1s
win+Meson test (0)	10m 37s
win+Meson test (7)	9m 13s
win+Meson test (6)	32m 57s
win+Meson test (5)	11m 55s
win+Meson test (4)	9m 3s
win+Meson test (2)	7m 41s
win+Meson test (9)	9m 32s
win+Meson test (8)	8m 59s
win+Meson test (3)	59m 15s
win+Meson test (1)	5m 53s
win test (4)	11m 14s
win test (2)	7m 8s
win test (5)	9m 43s
win test (7)	14m 33s
win test (8)	7m 12s
win test (0)	9m 38s
win test (1)	7m 56s
win test (3)	6m 59s
win test (6)	59m 20s
win test (9)	7m 27s
	21h 43m 44s

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