MAINTAINERS: Add docs/devel/testing/functional.rst to the functional section

Add an entry for docs/devel/testing/functional.rst to get notified
on patches that change this file.

Message-ID: <20250306105124.702131-1-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>

MAINTAINERS

@@ -4228,6 +4228,7 @@ Functional testing framework
 M: Thomas Huth <thuth@redhat.com>
 R: Philippe Mathieu-Daudé <philmd@linaro.org>
 R: Daniel P. Berrange <berrange@redhat.com>
+F: docs/devel/testing/functional.rst
 F: tests/functional/qemu_test/
 
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