Run tests with minimum required go version

This should help catch issues when minimum version is accidentally
bumped.

Author: jorgenpt

.github/workflows/test.yaml

@@ -5,7 +5,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-22.04, windows-2019]
-        go-ver: ["1.20"]
+        go-ver: ["1.19"]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3