t1400: have fifo test clean after itself #28426

Job	Run time
config	8s
fuzz smoke test	1m 12s
rust-analysis	1m 33s
win+Meson build	4m 47s
win build	4m 45s
sparse	3m 48s
static-analysis	5m 22s
documentation	7m 22s
osx-reftable (macos-14)	19m 52s
osx-meson (macos-14)	26m 32s
osx-clang (macos-14)	16m 34s
osx-gcc (macos-14)	19m 2s
linux-reftable (ubuntu:rolling)	1m 22s
linux-sha256 (ubuntu:rolling)	1m 29s
linux-asan-ubsan (ubuntu:rolling)	1m 24s
linux-TEST-vars (ubuntu:20.04)	12m 59s
linux32 (i386/ubuntu:focal)	9m 45s
linux-breaking-changes (ubuntu:rolling)	1m 12s
linux-leaks (ubuntu:rolling)	1m 8s
almalinux-8 (almalinux:8)	11m 8s
linux-musl-meson (alpine:latest)	8m 13s
fedora-breaking-changes-meson (fedora:latest)	1m 26s
linux-meson (ubuntu:rolling)	1m 18s
linux-reftable-leaks (ubuntu:rolling)	1m 12s
debian-11 (debian:11)	8m 12s
win+VS test	0s
win+VS build	0s
win+Meson test (9)	28s
win+Meson test (1)	28s
win+Meson test (6)	32s
win+Meson test (0)	39s
win+Meson test (2)	29s
win+Meson test (7)	49s
win+Meson test (3)	40s
win+Meson test (8)	31s
win+Meson test (5)	30s
win+Meson test (4)	30s
win test (1)	5m 50s
win test (6)	7m 8s
win test (9)	8m 35s
win test (4)	9m 59s
win test (2)	8m 18s
win test (0)	7m 22s
win test (5)	7m 14s
win test (7)	7m 45s
win test (8)	4m 47s
win test (3)	5m 40s
	4h 9m 59s

Provide feedback