Changing the build intermediate paths for gitlab-runner
Conceptually, this approach is not the way to go; the build directory is not a deployment directory, it's a temporary directory, to build or to deploy from, whereas on a shell executor this could be fixed.

So what you need is to deploy from that directory with a script as per gitlab-ci.yml below, to the correct directory of deployment.

stages:
- deploy

variables:
  TARGET_DIR: /home/ab12/public_html/$CI_PROJECT_NAME

deploy:
  stage: deploy
  script:
     mkdir -pv $TARGET_DIR
     rsync -r --delete ./ $TARGET_DIR
  tags:
    - myrunner


This will move your projectfiles in /home/ab12/public_html/

naming your projects as project1 .. projectn, all your projects could use this same .gitlab-ci.yml file.