Update .cirrus.yml

Author: amontoison

.cirrus.yml

@@ -5,13 +5,7 @@ task:
         image_family: freebsd-13-3
       env:
         matrix:
-          - JULIA_VERSION: 1.6
           - JULIA_VERSION: 1
-    - name: musl Linux
-      container:
-        image: alpine:3.14
-      env:
-        - JULIA_VERSION: 1
   install_script: |
     URL="https://raw.githubusercontent.com/ararslan/CirrusCI.jl/master/bin/install.sh"
     set -x