Checklist

• make -j8 test (UNIX), or vcbuild test nosign (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

tools

Description of change

Currently, there are a number of popups that get displayed when running
the tests asking to accept incoming network connections. Rules can be
added manually to the socket firewall on Mac OS X but getting this right
might not be obvious and quite a lot of time can be wasted trying to get
the rules right. This script hopes to simplify things a little so that
it can be re-run when needed.

The script should be runnable from both the projects root directory and
from the tools directory, for example:
$ sudo ./tools/macosx-firewall.sh

Fixes: #8911