change CI to only support julia 1.9 or newer

Author: AFeuerpfeil

.github/workflows/CI.yml

@@ -21,7 +21,7 @@ jobs:
       fail-fast: false
       matrix:
         version:
-          - '1.8' # lowest supported version
+          - '1.9' # lowest supported version
           - 'lts' # julia lts
           - '1' # latest stable 1.x release of Julia
         os: