Align with itk-dev drupal-11 Docker template

[jeppekroghitk]

Link to ticket

#7792

Description

This branch serves to adopt itk-dev drupal-11 Docker stack on PHP 8.4

Regarding the failing "Check that site can be updated"-action:

update-site first checks out develop (github.base_ref) and runs composer install against develop's old docker-compose.yml, which predates the COMPOSE_USER convention (no user: on phpfpm).

The container runs as root while the runner-owned bind mount rejects the write — In Filesystem.php line 261: /app/vendor does not exist and could not be created.

Nothing in this PR can affect develop's checkout, and it will stop failing after this branch is merged.

Security updates are handeled in a seperate PR #15

Screenshot of the result

N/A

Checklist

• My code is covered by test cases.
• My code passes our test (all our tests).
• My code passes our static analysis suite.
• My code passes our continuous integration process.