Update tests.yml

Author: ChrisRackauckas

.github/workflows/tests.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        julia-version: ["1", "1.6"]
+        julia-version: ["1"]
         julia-arch: [x64]
         os: [macos-latest, ubuntu-latest]