Disable proxy in container scanning template

closes https://gitlab.com/gitlab-org/gitlab-ee/issues/11105

changelogs/unreleased/11105-fix-cs-with-proxy.yml

+---
+title: Fix proxy support in Container Scanning
+merge_request: 27246
+author:
+type: fixed

lib/gitlab/ci/templates/Security/Container-Scanning.gitlab-ci.yml

@@ -23,6 +23,9 @@ container_scanning:
     DOCKER_HOST: tcp://${DOCKER_SERVICE}:2375/
     # https://hub.docker.com/r/arminc/clair-local-scan/tags
     CLAIR_LOCAL_SCAN_VERSION: v2.0.8_fe9b059d930314b54c78f75afe265955faf4fdc1
+    ## Disable the proxy for clair-local-scan, otherwise Container Scanning will
+    ## fail when a proxy is used.
+    NO_PROXY: ${DOCKER_SERVICE},localhost
   allow_failure: true
   services:
     - docker:stable-dind