[Config][Exception] Improve Routing Syntax Import Error



| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11300
| License       | MIT
| Doc PR        | n/a
I'm not sure we need the period here, but perhaps other people disagree. At the very least, this should come *after* the `(which is ...)` parts.