For the next soul looking for an answer, I managed to solve the issue with the next 2 Init scripts, it gets tricky in the apt or apt-get, that was the issue, sometimes it did update, sometimes it didn't, making it possible to find libmysqlclient21.

1)

%sh

sudo rm -r /var/lib/apt/lists/* 

sudo apt clean && 

  sudo apt update --fix-missing -y &&

  sudo apt install -y libmysqlclient21

sudo apt install -y gdal-bin

2)

%sh

sudo apt --fix-missing -y update --fix-missing

sudo apt-get install -y libudunits2-dev libproj-dev libgeos-dev libgdal-dev