gitlab-ci: Run make distcheck in autotools build & test job

We don't set the PIGLIT_DIR and XTS_DIR environment variables for make
distcheck for now, otherwise it complains about files left behind by
piglit.
3 jobs for gitlab-ci-distheck in 3 minutes (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #133753
debian-testing

00:00:15

 
  Build And Test
passed #133754
autotools-build-and-test

00:02:45

passed #133755
meson-build-and-test

00:00:43