Disable safe.directory git checks in the container image

[WojciechMazur]

git config --system --add safe.directory $PWD is required in our setup when using containers in the CI. However, setting it once per job is not enough - it is not persisted between steps.

It coused problems during 3.6.3-RC1 release - https://github.com/scala/scala3/actions/runs/12253895253/job/34194840440#step:15:25

It also leads to swallowed exceptions when republishing SDK https://github.com/scala/scala3/actions/runs/12253895253/job/34194840440#step:15:25

It is also a blocker for tests in LTS fork, in safe directory should be set to $PWD in every fork - https://github.com/scala/scala3-lts/pull/23/files

We can disabled the safe.directory checks globally in the published docker image.
Tested in a fork repository: https://github.com/WojciechMazur/dotty/pull/2/checks

Before merging requires:

• - Publishing new version of lampepfl:dotty container image
• - Updating CI in this branch to use updated container image