Remove Debian bullseye jobs

The Debian bullseye has reached end-of-life, remove it from the CI.

.gitlab-ci.yml

@@ -147,10 +147,6 @@ stages:
 
 # Debian
 
-.debian-bullseye-amd64: &debian_bullseye_amd64_image
-  image: "$CI_REGISTRY_IMAGE:debian-bullseye-amd64"
-  <<: *linux_amd64
-
 .debian-bookworm-amd64: &debian_bookworm_amd64_image
   image: "$CI_REGISTRY_IMAGE:debian-bookworm-amd64"
   <<: *linux_amd64
@@ -1316,52 +1312,6 @@ unit:clang:tsan:
     - job: clang:tsan
       artifacts: true
 
-# Jobs for Debian 11 "bullseye" (amd64)
-
-clang:bullseye:amd64:
-  variables:
-    CC: ${CLANG}
-    CFLAGS: "${CFLAGS_COMMON} -Wenum-conversion"
-  <<: *debian_bullseye_amd64_image
-  <<: *build_job
-
-system:clang:bullseye:amd64:
-  <<: *debian_bullseye_amd64_image
-  <<: *system_test_job
-  needs:
-    - job: clang:bullseye:amd64
-      artifacts: true
-
-unit:clang:bullseye:amd64:
-  <<: *debian_bullseye_amd64_image
-  <<: *unit_test_job
-  needs:
-    - job: clang:bullseye:amd64
-      artifacts: true
-
-gcc:bullseye:amd64:
-  variables:
-    CC: gcc
-    CFLAGS: "${CFLAGS_COMMON}"
-    # See https://gitlab.isc.org/isc-projects/bind9/-/issues/3444
-    EXTRA_CONFIGURE: "--with-libidn2 --without-jemalloc --disable-leak-detection"
-  <<: *debian_bullseye_amd64_image
-  <<: *build_job
-
-system:gcc:bullseye:amd64:
-  <<: *debian_bullseye_amd64_image
-  <<: *system_test_job
-  needs:
-    - job: gcc:bullseye:amd64
-      artifacts: true
-
-unit:gcc:bullseye:amd64:
-  <<: *debian_bullseye_amd64_image
-  <<: *unit_test_job
-  needs:
-    - job: gcc:bullseye:amd64
-      artifacts: true
-
 # Jobs for Clang builds on Debian 12 "bookworm" (amd64)
 
 clang:bookworm:amd64: