use new sbt 1.7 feature to not repeat Scala version numbers

Author: SethTisue

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
       fail-fast: false
       matrix:
         java: [8, 11, 17]
-        scala: [2.11.12, 2.12.15, 2.13.8, 3.1.2]
+        scala: [2.11.x, 2.12.x, 2.13.x, 3.x]
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2