vscode-extensions: add `cacert` to update script

pkgs/applications/editors/vscode/extensions/update_installed_exts.sh

···
 #! /usr/bin/env nix-shell
-#! nix-shell -i bash -p curl jq unzip
+#! nix-shell -i bash -p cacert curl jq unzip
 # shellcheck shell=bash
 set -eu -o pipefail