Document errorLabels option for failCommand fail point.

source/unified-test-format/unified-test-format.rst

@@ -3892,6 +3892,7 @@ The ``failCommand`` fail point may be configured like so::
           failCommands: [<string>, ...],
           closeConnection: <boolean>,
           errorCode: <integer>,
+          errorLabels: [<string>, ...],
           writeConcernError: <object>,
           appName: <string>,
           blockConnection: <boolean>,
@@ -3909,6 +3910,10 @@ if desired:
 * ``errorCode``: Optional integer, which is unset by default. If set, the
   command will not be executed and the specified command error code will be
   returned as a command error.
+* ``errorLabels``: Optional array of strings. If set, this list overrides the
+  server's normal behavior for adding error labels. An empty array may be used
+  to suppress the server from adding error labels to the response. New in server
+  4.3.1 (`SERVER-43941 <https://jira.mongodb.org/browse/SERVER-43941>`__).
 * ``appName``: Optional string, which is unset by default. If set, the fail
   point will only apply to connections for MongoClients created with this
   ``appname``. New in server 4.4.0-rc2
@@ -4061,6 +4066,7 @@ Changelog
 ..
   Please note schema version bumps in changelog entries where applicable.
 
+:2024-01-02: Document ``errorLabels`` option for ``failCommand`` fail point.
 :2023-10-04: **Schema version 1.17.**
              Add ``serverHeartbeatStartedEvent``, ``serverHeartbeatSucceededEvent``, and
              ``serverHeartbeatFailedEvent`` for asserting on SDAM server heartbeat events.