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

x11proto 2020.1 provides DPMS 1.2.
4 jobs for dpms in 5 minutes and 20 seconds (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #2359445
debian-testing

00:00:15

 
  Build And Test
passed #2359446
autotools

00:05:04

failed #2359447
meson

00:00:59

failed #2359448
meson-noglamor

00:01:12

 
Name Stage Failure
failed
meson Build And Test
no input file                        383
cleanups performed 0
files in cache 59913
cache size 2.9 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-noglamor Build And Test
cleanups performed                     0
files in cache 29036
cache size 1.4 GB
max cache size 5.0 GB
Uploading artifacts for failed job
Uploading artifacts...
WARNING: build/test/piglit-results/: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1