Add v1.6 to CI

Author: jonniedie

.github/workflows/ci.yml

@@ -19,6 +19,7 @@ jobs:
           - '1.3'
           - '1.4'
           - '1.5'
+          - '1.6'
           - '1' # Leave this line unchanged. '1' will automatically expand to the latest stable 1.x release of Julia.
           - 'nightly'
         os: