Merge pull request rails#51867 from duffuniverse/add-missed-comma-to-…

…instrumentation-guide

[ci skip] Add a comma in the Exceptions section of Active Support Instrumentation guide

guides/source/active_support_instrumentation.md

@@ -925,7 +925,7 @@ This event is only emitted when using the Google Cloud Storage service.
 Exceptions
 ----------
 
-If an exception happens during any instrumentation the payload will include
+If an exception happens during any instrumentation, the payload will include
 information about it.
 
 | Key                 | Value                                                          |