circleci: Ignore varnishstatdiff on Alpine Linux

There seems to be no output right now, and the test case is failing.

.circleci/config.yml

@@ -438,7 +438,7 @@ workflows:
           name: build_alpine
           dist: alpine
           release: "latest"
-          #extra_conf: --without-jemalloc
+          extra_conf: --without-contrib
       - build:
           name: build_archlinux
           dist: archlinux