Make sure not to use apt in the workflows that use flatpak-platform docker images

### Problem

In #234, we rebased `ghcr.io/elementary/flatpak-platform/runtime` docker image on Flathub action image that doesn't ship with apt, so the `Install git, python3-git and jq` step:

```yml
gettext:
name: Gettext
runs-on: ubuntu-latest
container:
image: ghcr.io/elementary/flatpak-platform/runtime:8.2-x86_64
options: --privileged

steps:
- name: Install git, python3-git and jq
run: |
apt-get update # this will fail!
apt-get install git jq python3-git -y
```

will fail: https://github.com/elementary/calculator/actions/runs/24336768166/job/74193731827

```
Run apt-get update
apt-get update
apt-get install git jq python3-git -y
shell: sh -e {0}
/__w/_temp/7466f102-0a3e-4bb3-ba8c-c108f682fe6d.sh: line 1: apt-get: command not found
Error: Process completed with exit code 127.
```

### Proposal

Make sure not to use apt in the workflows that use flatpak-platform docker images.

### Prior Art (Optional)

_No response_