upload-pack: send keepalive while feeding pack-objects #28754

Job	Run time
config	8s
fuzz smoke test	1m 5s
win build	5m 10s
static-analysis	6m 2s
rust-analysis	1m 38s
osx-meson (macos-14)	59m 15s
documentation	7m 24s
win+Meson build	4m 28s
osx-clang (macos-14)	6h 0m 19s
osx-reftable (macos-14)	34m 40s
sparse	4m 2s
debian-11 (debian:11)	21m 55s
linux-reftable (ubuntu:rolling)	24m 0s
osx-gcc (macos-14)	6h 0m 18s
linux-musl-meson (alpine:latest)	21m 16s
linux-TEST-vars (ubuntu:20.04)	24m 22s
linux-leaks (ubuntu:rolling)	49m 6s
almalinux-8 (almalinux:8)	19m 59s
fedora-breaking-changes-meson (fedora:latest)	21m 13s
linux32 (i386/ubuntu:20.04)	6h 0m 3s
linux-asan-ubsan (ubuntu:rolling)	1h 11m 33s
linux-breaking-changes (ubuntu:rolling)	25m 0s
linux-reftable-leaks (ubuntu:rolling)	47m 33s
linux-sha256 (ubuntu:rolling)	25m 15s
linux-meson (ubuntu:rolling)	25m 21s
win+VS test	0s
win+VS build	0s
win+Meson test (2)	45m 38s
win+Meson test (7)	6m 29s
win+Meson test (8)	10m 25s
win+Meson test (0)	8m 28s
win+Meson test (5)	9m 11s
win+Meson test (9)	6m 32s
win+Meson test (1)	6m 14s
win+Meson test (3)	11m 18s
win+Meson test (6)	13m 29s
win+Meson test (4)	18m 41s
win test (0)	11m 22s
win test (4)	46m 49s
win test (8)	6m 18s
win test (5)	6m 57s
win test (2)	7m 39s
win test (3)	9m 34s
win test (9)	4m 31s
win test (7)	7m 5s
win test (1)	7m 53s
win test (6)	39m 38s
	1d 7h 5m 16s

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