fix c example build error (#2905)

Author: jeff-allen-mongo

source/includes/driver-examples/driver-example-transactions-retry-2.rst

@@ -127,7 +127,7 @@
          .. literalinclude:: /driver-examples/test-mongoc-sample-commands.c 
             :language: c
             :start-after: commit transactions with retry logic
-            :end-before: updates two collections in a transaction 
+            :end-before: updates two collections in a transaction and calls commit_with_retry
 
      - id: cpp
        content: |