Changes

jobs/ttcn3: …-pablo-gtp: don't wipe workspace

The ttcn3-ggsn-test-kernel-* jobs should not wipe their workspace, so we
can avoid shallow-cloning the kernel if the commit did not change.

The way the scripts in docker-playground.git are written, this also
caused a permission error.

Change-Id: I4ac1b2c3f5ba63c131dd1d6a4888f32a27264eba

ttcn3-ggsn-test-kernel-latest-net-next: update net-next branch

The branch of net-next is now called main. By using the old name, the
jenkins job was checking out a 6.3 kernel, we are now at 6.9 rcs.

Related: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/
Change-Id: Ieee448c514bc0ff457b9d17c8b12ee00953995d2