Update minimum Julia version to 1.6 in CI config

Author: arturgower

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       fail-fast: false
       matrix:
         version:
-          - '1.2' # Replace this with the minimum Julia version that your package supports. E.g. if your package requires Julia 1.5 or higher, change this to '1.5'.
+          - '1.6' # Replace this with the minimum Julia version that your package supports. E.g. if your package requires Julia 1.5 or higher, change this to '1.5'.
           - '1' # Leave this line unchanged. '1' will automatically expand to the latest stable 1.x release of Julia.
           - 'nightly'
         os:
@@ -53,7 +53,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: julia-actions/setup-julia@v1
         with:
-          version: '1.5'
+          version: '1.6'
       - run: |
           julia --project=docs -e '
             using Pkg