src:nftables: add salsa CI support

Following docs at:
 https://salsa.debian.org/salsa-ci-team/pipeline/blob/master/README.md

Signed-off-by: Arturo Borrero Gonzalez <arturo@debian.org>
6 jobs for master in 8 minutes and 51 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #185871
build

00:03:36

 
  Test
failed #185874
autopkgtest

00:03:18

passed #185875
blhc

00:01:34

passed #185873
lintian

00:02:05

passed #185876
piuparts

00:05:14

passed #185872
reprotest

00:04:08

 
Name Stage Failure
failed
autopkgtest Test
autopkgtest [04:26:48]: @@@@@@@@@@@@@@@@@@@@ summary
command1 PASS
internaltest-shell.sh PASS
internaltest-monitor.sh FLAKY non-zero exit status 1
systemd-service-test.sh FAIL non-zero exit status 1
autopkgtest [04:26:48]: Binaries: resetting testbed apt configuration
Hit:1 http://cdn-fastly.deb.debian.org/debian unstable InRelease
Reading package lists...
ERROR: Job failed: exit code 1