update CI versions to Julia 1.11 (current) and 1.10 LTS (#809)

Author: colinleach

.github/workflows/exercise-tests.yml

@@ -22,11 +22,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        julia-version: ["1.6", "1", nightly]
+        julia-version: ["1.10", "1.11", nightly]
         os: [ubuntu-22.04, windows-2022, macos-14]
-        exclude:
-          - julia-version: 1.6
-            os: macos-14
 
     steps:
       - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332