remove alpine 3.21 integration test

Author: pdabelf5

.github/workflows/ci.yml

@@ -160,11 +160,6 @@ jobs:
     strategy:
       matrix:
         container:
-        - image: "alpine"
-          version: "3.21"
-          plus: "r33"
-          release: "alpine"
-          path: "/nginx-plus/agent"
         - image: "alpine"
           version: "3.20"
           plus: "r32"