doc: Test-by?

Commonly used is "Tested-by."

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/SubmittingPatches

@@ -405,7 +405,7 @@ person it names.  This tag documents that potentially interested parties
 have been included in the discussion
 
 
-14) Using Test-by: and Reviewed-by:
+14) Using Tested-by: and Reviewed-by:
 
 A Tested-by: tag indicates that the patch has been successfully tested (in
 some environment) by the person named.  This tag informs maintainers that