Test on Go 1.22, drop old versions

The Go team officially supports the two latest releases, so we're even
being generous here.

Go 1.17 notably lacks useful strings.Cut function.

.github/workflows/ci.yml

@@ -15,9 +15,10 @@ jobs:
       max-parallel: 4
       matrix:
         go: [
+          "1.22",
+          "1.21",
+          "1.20",
           "1.19",
-          "1.18",
-          "1.17",
         ]
 
     steps:
@@ -46,9 +47,10 @@ jobs:
       max-parallel: 4
       matrix:
         go: [
+          "1.22",
+          "1.21",
+          "1.20",
           "1.19",
-          "1.18",
-          "1.17",
         ]
 
     steps: