ci: remove using Docker container in source.yml

In this commit, we're fixing a problem with Docker in the workflow
`.github/workflows/source.yml`.

The mentioned workflow uses the `.github/actions/environment` action
that needs a permission to make a loopback device for [1]. We didn't
allow for that before due to missing container args, and it caused the
following error:

```
umount: /tmp/luajit-test-vardir: must be superuser to unmount.
256000+0 records in
256000+0 records out
1048576000 bytes (1.0 GB, 1000 MiB) copied, 1.36702 s, 767 MB/s
mount: /tmp/luajit-test-vardir: mount failed: Operation not permitted.
Error: Process completed with exit code 1.
```

The problem started since commit af996bbb ("ci: dockerize
linux workflows"). The simplest way to fix the issue is not to run
the workflow inside a Docker container because a tarball with the
source code is created via the `./packpack/packpack tarball` command
that runs a Docker container as well.

[1] https://github.com/tarantool/tarantool/issues/7472

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci

(cherry picked from commit 09ad57f4)