fix: inaccurate Server-Timing durations

The transaction duration was notably off, doing:

```
curl localhost:3000/rpc/sleep?seconds=5 -i
```

Shows `46.1` for the `transaction;dur`, with this fix we obtain
`5007.3`.

Fixes https://github.com/PostgREST/postgrest/issues/4522

This also fixes inaccurate "schema cache queried" logs,
see https://github.com/PostgREST/postgrest/issues/4551.

src/PostgREST/Observation.hs

@@ -156,7 +156,7 @@ observationMessage = \case
     "Evicted entry from JWT cache"
   where
     showMillis :: Double -> Text
-    showMillis x = toS $ showFFloat (Just 1) (x * 1000) ""
+    showMillis x = toS $ showFFloat (Just 1) x ""
 
     jsonMessage err = T.decodeUtf8 . LBS.toStrict . Error.errorPayload $ Error.PgError False err