Revert for 258.3 of https://github.com/systemd/systemd/pull/39945 as that
commit got backported. It fails because master has the kernel install moved
to /var/tmp and this test change assumed that.

--- a/src/kernel-install/test-kernel-install.sh
+++ b/src/kernel-install/test-kernel-install.sh
@@ -318,7 +318,7 @@ diff -u <(echo "$output") - >&2 <<EOF
 		"KERNEL_INSTALL_LAYOUT=other",
 		"KERNEL_INSTALL_INITRD_GENERATOR=none",
 		"KERNEL_INSTALL_UKI_GENERATOR=",
-		"KERNEL_INSTALL_STAGING_AREA=${TMPDIR:-/tmp}/kernel-install.staging.XXXXXX"
+		"KERNEL_INSTALL_STAGING_AREA=/tmp/kernel-install.staging.XXXXXX"
 	]
 }
 EOF