abuild: make sure to not get colors in git_last_commit

git log may return color codes if users colored output forcibly enabled
with:

[color]
	ui = always

Use `git rev-list` instead of `git log` to make sure that we don't get
any color codes.

fixes https://gitlab.alpinelinux.org/alpine/abuild/-/issues/10042

abuild.in

@@ -951,7 +951,7 @@ git_dirty() {
 
 # echo last commit hash id
 git_last_commit() {
-	$git log --format=oneline -n 1 -- "$startdir" | awk '{print $1}'
+	$git rev-list -n 1 HEAD -- "$startdir"
 }
 
 # date of last commit