fix(api): record the retirement against the release that carries it

v1.38.19 was cut before this change and still answers on the path, so
naming it as the version that removed the route would be wrong in the
published contract from the day it appears.

docs/api/openapi.yaml

@@ -20425,9 +20425,9 @@ paths:
       deprecated: true
       tags:
         - Retired
-      summary: POST /api/auth/check-user — removed in v1.38.19
+      summary: POST /api/auth/check-user — removed in v1.38.20
       description: >-
-        Removed in v1.38.19. Every request to this path answers 410 Gone, whatever the method and whatever credential it
+        Removed in v1.38.20. Every request to this path answers 410 Gone, whatever the method and whatever credential it
         carries. There is no replacement; the capability is gone rather than moved.
 
 
@@ -20443,7 +20443,7 @@ paths:
         do not offer a retry.
       responses:
         "410":
-          description: The path was removed in v1.38.19 and will not answer again. `meta.errorCode` = `route.retired`,
+          description: The path was removed in v1.38.20 and will not answer again. `meta.errorCode` = `route.retired`,
             `meta.removedIn` carries the version, and `meta.replacedBy` carries the replacement path or null.
           content:
             application/json: