update and simplify cirrus config

Author: dpo

.cirrus.yml

@@ -5,18 +5,7 @@ task:
         image_family: freebsd-14-2
       env:
         matrix:
-          - JULIA_VERSION: 'lts'
           - JULIA_VERSION: '1'
-    - name: musl Linux
-      container:
-        image: alpine:3.14
-      env:
-        - JULIA_VERSION: 1
-    - name: MacOS M1
-      macos_instance:
-        image: ghcr.io/cirruslabs/macos-monterey-base:latest
-      env:
-        - JULIA_VERSION: 1
   install_script: |
     URL="https://raw.githubusercontent.com/ararslan/CirrusCI.jl/master/bin/install.sh"
     set -x