Merge branch 'ondrej/remove-distros-near-eol' into 'main'

Remove CentOS 6 from GitLab CI, it will EOL before BIND 9.18 is released

See merge request isc-projects/bind9!3799

.gitlab-ci.yml

@@ -74,10 +74,6 @@ stages:
 
 # CentOS
 
-.centos-centos6-amd64: &centos_centos6_amd64_image
-  image: "$CI_REGISTRY_IMAGE:centos-centos6-amd64"
-  <<: *linux_amd64
-
 .centos-centos7-amd64: &centos_centos7_amd64_image
   image: "$CI_REGISTRY_IMAGE:centos-centos7-amd64"
   <<: *linux_amd64
@@ -536,30 +532,6 @@ unit:gcc:alpine3.12:amd64:
     - job: gcc:alpine3.12:amd64
       artifacts: true
 
-# Jobs for regular GCC builds on CentOS 6 (amd64)
-
-gcc:centos6:amd64:
-  variables:
-    CC: gcc
-    CFLAGS: "${CFLAGS_COMMON}"
-    EXTRA_CONFIGURE: "--with-libidn2 --disable-warn-error"
-  <<: *centos_centos6_amd64_image
-  <<: *build_job
-
-system:gcc:centos6:amd64:
-  <<: *centos_centos6_amd64_image
-  <<: *system_test_job
-  needs:
-    - job: gcc:centos6:amd64
-      artifacts: true
-
-unit:gcc:centos6:amd64:
-  <<: *centos_centos6_amd64_image
-  <<: *unit_test_job
-  needs:
-    - job: gcc:centos6:amd64
-      artifacts: true
-
 # Jobs for regular GCC builds on CentOS 7 (amd64)
 
 gcc:centos7:amd64: