rename ci and restore julia lts version

Author: Jutho

.github/workflows/ci.yml .github/workflows/CI.yml.github/workflows/ci.yml renamed to .github/workflows/CI.yml

@@ -21,7 +21,7 @@ jobs:
       fail-fast: false
       matrix:
         version:
-          - '1.8' # LTS version
+          - '1.6' # LTS version
           - '1' # automatically expands to the latest stable 1.x release of Julia
         os:
           - ubuntu-latest