test: Use g_get_tmp_dir() #924

Job	Run time
OS (apt-docker.io/amd64/ubuntu:devel)	1m 48s
OS (apt-docker.io/amd64/ubuntu:latest)	2m 1s
OS (apt-docker.io/amd64/ubuntu:rolling)	2m 4s
OS (apt-docker.io/i386/debian:testing)	1m 57s
OS (apt-docker.io/amd64/debian:testing)	1m 51s
OS (dnf-registry.fedoraproject.org/fedora:latest)	2m 33s
OS (dnf-registry.fedoraproject.org/fedora:rawhide)	2m 40s
OS (alpine-docker.io/alpine)	26s
OS (alpine-docker.io/i386/alpine)	27s
OS ([email protected]/alpine)	26s
OS (nix-docker.io/nixos/nix)	1m 6s
OS (gentoo-)	8m 45s
OS (alpine@gudev-alpine, EXTRA_PACKAGES=libgudev-dev)	30s
	26m 34s

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