ci/container: Include DEBIAN_BUILD_TAG in debian/arm64_build

Unlike other containers (e.g. debian/x86_64_build-base and
debian/x86_64_build), debian/arm64_build is a single-stage image without
a separate -base variant.

Including DEBIAN_BUILD_TAG in its FDO_DISTRIBUTION_TAG ensures it gets
rebuilt when the build tag changes.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/12737
Signed-off-by: Valentine Burley <valentine.burley@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35000>

.gitlab-ci/container/debian/arm64_build.sh

@@ -1,6 +1,10 @@
 #!/usr/bin/env bash
 # shellcheck disable=SC2086 # we want word splitting
 
+# When changing this file, you need to bump the following
+# .gitlab-ci/image-tags.yml tags:
+# DEBIAN_BUILD_TAG
+
 set -e
 
 . .gitlab-ci/setup-test-env.sh

.gitlab-ci/container/gitlab-ci.yml

@@ -273,7 +273,7 @@ debian/arm64_build:
   tags:
     - $FDO_RUNNER_JOB_PRIORITY_TAG_AARCH64
   variables:
-    MESA_IMAGE_TAG: &debian-arm64_build "${DEBIAN_BASE_TAG}--${PKG_REPO_REV}"
+    MESA_IMAGE_TAG: &debian-arm64_build "${DEBIAN_BUILD_TAG}--${DEBIAN_BASE_TAG}--${PKG_REPO_REV}"
     LLVM_VERSION: &debian-arm64-llvm 19
 
 .use-debian/arm64_build: