gitlab-ci: Bump DEBIAN_TAG to update x11proto-dev for DPMS

x11proto 2020.1 provides DPMS 1.2.
4 jobs for dpms in 12 minutes and 57 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Docker Image
passed #2359362
debian-testing

00:06:07

 
  Build And Test
passed #2359363
autotools

00:06:49

failed #2359364
meson

00:01:01

failed #2359365
meson-noglamor

00:01:02

 
Name Stage Failure
failed
meson-noglamor Build And Test
no input file                        304
cleanups performed 0
files in cache 25146
cache size 1.3 GB
max cache size 5.0 GB
Uploading artifacts...
WARNING: build/test/piglit-results/: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1
failed
meson Build And Test
no input file                        304
cleanups performed 0
files in cache 25146
cache size 1.3 GB
max cache size 5.0 GB
Uploading artifacts...
WARNING: build/test/piglit-results/: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1