__format_topdir() accepts "absolute", "relative", "unaltered", and
"make:<variable-name>", but the error message it raises for anything
else only lists "unaltered", "absolute", and
"make:<variable-name>", leaving out "relative".
Add "relative" to the list of valid formats in the error message.
Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.84.2
Signed-off-by: Jan Lindemann <jan@janware.com>