Specify latest Go patch release in go.mod

Annoyingly, the setup-go action we use in CI takes the exact version
number from go.mod by default, so it makes sense to keep this somewhat
more up-to-date that we might otherwise, given that it's supposed to be
a minimum version constraint and not a specific version. Sigh.

go.mod

@@ -1,6 +1,6 @@
 module github.com/alphagov/router
 
-go 1.22.0
+go 1.22.2
 
 require (
 	github.com/getsentry/sentry-go v0.27.0