Prevent bmake from installing security/ca-certificates

[P Gman <patrickgunsolley%gmail.com@localhost>]

Hello everyone

On my Debian Trixie machine, I've linked my system ca-certificates
into my pkg tree in order to avoid potential conflicts and
duplication.

I'd like to ensure that the pkgsrc ca-certificates wont get built and
installed, whether accidentally (or by another tenant) or as a
dependency, overwriting this.

Is there a recommended way to do this?

Cheers