zsh:funcs:git-checkout-worktree: Remove -p flag

As under OSX the -p flag does not exist, it seems safer to just use
`mktemp -d` and create the worktree under that directory.
This just has the disadvantage of one more dir to display in the `PWD`.

.config/zsh/zshrc.d/40-functions.zsh

@@ -379,18 +379,21 @@ nvim-man() {
 # Creates a git worktree checking it out the first argument in a temporary
 # directory that is deleted again, if the spawned subshell exits.
 git-checkout-worktree() {
-	local GIT_ROOT TEMP_DIR
+	local GIT_ROOT TEMP_DIR REPO_DIR
 	GIT_ROOT="$(basename "$(git rev-parse --show-toplevel)")" || return
-	TEMP_DIR="$(mktemp -dp "${TMPDIR:-/tmp}" "$GIT_ROOT.XXXXX")"
+	TEMP_DIR="$(mktemp -d)"
+	REPO_DIR="$TEMP_DIR/$GIT_ROOT"
 
-	git worktree add "$TEMP_DIR" "$1"
-	pushd -q "$TEMP_DIR"
+	git worktree add "$REPO_DIR" "$1"
+	pushd -q "$REPO_DIR"
 
 	# Start subshell
 	"$SHELL"
 
 	# Cleanup when exiting
 	popd -q
-	git worktree remove "$TEMP_DIR"
+	git worktree remove "$REPO_DIR"
 	git worktree prune
+
+	command rm -rf "$TEMP_DIR"
 }