Skip checking for `zeek` binary for some commands

[timwoj]

The zkg commands in the script to update the packages listing for package.zeek.org prints out the following with every invocation:

2025-01-13 21:52:49 WARNING unable to discover builtin-packages: No "zeek" executable in PATH

None of the commands that it needs to run require a zeek binary to exist, yet zkg checks every time and complains.