fix: make ci happy

Author: fumiama

.github/workflows/unitest.yml

@@ -17,7 +17,6 @@ jobs:
       run: |
         df -h
 
-        docker rmi `docker images -q`
         sudo rm -rf /usr/share/dotnet /etc/mysql /etc/php /etc/apt/sources.list.d
         sudo -E apt-get -y purge azure-cli ghc* zulu* hhvm llvm* firefox google* dotnet* powershell openjdk* mysql* php* android*
         sudo -E apt-get update