Adjust test matrix

The Indexes package uses the Artifacts framework, which is first available in Julia v1.3.

Author: CiaranOMara

.github/workflows/UnitTests.yml

@@ -12,7 +12,7 @@ jobs:
       fail-fast: false
       matrix:
         julia-version:
-          - '1.0' # LTS
+          - '1.3' # The Indexes package uses the Artifacts framework, which is first available in Julia 1.3.
           - '1'
         julia-arch: [x64, x86]
         os: [ubuntu-latest, windows-latest, macOS-latest]