build: Test against Go 1.22.

This updates CI to test against Go 1.22 and removes the tests for Go
1.20 accordingly.

Author: davecgh

.github/workflows/go.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go: ["1.20", "1.21"]
+        go: ["1.21", "1.22"]
     steps:
       - name: Check out source
         uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 #v4.1.1