tests/installer: Rename simpleUefiGummiboot -> simpleUefiSystemdBoot

It hasn't been called Gummiboot for ages.

Changed files
+1 -1
nixos
+1 -1
nixos/tests/installer.nix
···
};
# Simple GPT/UEFI configuration using systemd-boot with 3 partitions: ESP, swap & root filesystem
-
simpleUefiGummiboot = makeInstallerTest "simpleUefiGummiboot"
+
simpleUefiSystemdBoot = makeInstallerTest "simpleUefiSystemdBoot"
{ createPartitions =
''
$machine->succeed(