gitlab-ci: update the image version

We get newer CA certificates, to get rid of the annoying issues with the
now-expired Let's Encrypt root certificate.

Suggested-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Romain Naour <romain.naour@gmail.com>
Tested-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

.gitlab-ci.yml

@@ -1,7 +1,7 @@
 # Configuration for Gitlab-CI.
 # Builds appear on https://gitlab.com/buildroot.org/buildroot/pipelines
 
-image: buildroot/base:20200814.2228
+image: buildroot/base:20211120.1925
 
 stages:
   - generate-gitlab-ci