api-ref: Adjust BFV rescue non-support note.

Rescuing BFV instances became a thing in 2.87. Fix our api-ref.

Change-Id: I9c4fbea53b05490cf05ebd311b25791fa191af16

Author: notartom

api-ref/source/servers-actions.inc

@@ -755,7 +755,8 @@ Rescue Server (rescue Action)
 
 Puts a server in rescue mode and changes its status to ``RESCUE``.
 
-.. note:: This API is not supported for volume-backed instances.
+.. note:: Until microversion 2.87, this API is not supported for volume-backed
+          instances.
 
 Specify the ``rescue`` action in the request body.