docker: deprecate Ubuntu 18.04

Co-authored-by: Ruoyu Zhong <[email protected]>

.github/workflows/docker.yml

@@ -79,6 +79,10 @@ jobs:
               "homebrew/ubuntu${{matrix.version}}:master"
             )
           fi
+          if [[ "${{ matrix.version }}" == "18.04" ]]; then
+            # odeprecated: remove this in Homebrew >=4.4
+            echo "homebrew/ubuntu18.04:master is deprecated and will soon be retired. Use homebrew/ubuntu22.04:master or homebrew/ubuntu24.04 or homebrew/ubuntu20.04 or homebrew/brew. For CI, homebrew/ubuntu22.04:master is recommended." > .docker-deprecate
+          fi
 
           {
             if [[ "${#tags[@]}" -ne 0 ]]; then