Fix up clang-format CI.
diff --git a/ci/checkformat.gitlab-ci.yml b/ci/checkformat.gitlab-ci.yml
index c4b4c8e..588ec2e 100644
--- a/ci/checkformat.gitlab-ci.yml
+++ b/ci/checkformat.gitlab-ci.yml
@@ -5,7 +5,8 @@
     - merge_requests
   allow_failure: true
   before_script:
+    - export DEBIAN_FRONTEND=noninteractive
     - apt-get update -y
-    - apt-get install -y --no-install-recommends git clang-format-17
+    - apt-get install -y --no-install-recommends git clang-format clang-format-17
   script:
     - git clang-format-17 --diff --commit ${CI_MERGE_REQUEST_DIFF_BASE_SHA}