move all CI/CD to go1.18 (#15401)

.github/workflows/iam-integrations.yaml

@@ -61,7 +61,7 @@ jobs:
       # are turned off - i.e. if ldap="", then ldap server is not enabled for
       # the tests.
       matrix:
-        go-version: [1.17.x]
+        go-version: [1.18.x]
         ldap: ["", "localhost:389"]
         etcd: ["", "http://localhost:2379"]
         openid: ["", "http://127.0.0.1:5556/dex"]