git:checkout-worktree: Escape slashes in branch

Escape slashes in the branch name before passing it to `mktemp`.
Otherwise it would complain with:

    mktemp: invalid suffix [...], contains directory separator

.config/zsh/autoload/git/git-checkout-worktree

@@ -28,7 +28,7 @@ emulate -L zsh -o err_return -o no_unset
 
 local REPO_NAME WORKTREE_PATH
 REPO_NAME="${$(git rev-parse --show-toplevel):t}"
-WORKTREE_PATH="$(mktemp -d -p "" "worktree.XXX.$REPO_NAME.$1")"
+WORKTREE_PATH="$(mktemp -d -p "" "worktree.XXX.$REPO_NAME.${1//\//_}")"
 
 trap '
 	errc=$?