Add PHP 8.3 support

[salamzadeh]

I added support for PHP 8.3 and successfully built the Docker image using:

docker build . -t xampp-build

However, I noticed that the documentation refers to a folder named ../xampp-code:

docker run -v `pwd`/../xampp-code:/home/xampp-code \
           -v `pwd`/tarballs:/tmp/tarballs \
           -it xampp-build bash

I could not find any repository named xampp-code in the ApacheFriends organization.
Could you clarify where the actual XAMPP source code is expected to come from, or how the xampp-code directory should be prepared?