Add go 1.22 to CI

It's the latest version, several years newer than the version we were
previously testing, and I expect it to be the one shipped with the next
Ubuntu LTS so it's a good one to test. Keep 1.18 around as it's the
version shipped with the *previous* Ubuntu LTS and so is worth testing
as long as it's supported.

.github/workflows/golang-ci.yml

@@ -7,7 +7,10 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: [1.13, 1.18]
+        go-version:
+          - 1.13
+          - 1.18
+          - 1.22
 
     steps:
       - uses: actions/checkout@v3