build: bump minimum go version for tests to 1.20 (#97)

Go only supports the three last major versions. That means that
Go 1.19 is no longer supported. This removes Go 1.19 from the
set of Go versions that is used for testing, and adds 1.20, 1.21,
and 1.22.

.github/workflows/unit-tests.yml

@@ -8,7 +8,7 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: [1.19.x, 1.21.x]
+        go-version: [1.20.x, 1.21.x, 1.22.x]
         os: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.os }}
     steps: