ref-manual: add missing TESTIMAGE_FAILED_QA_ARTIFACTS

This variable lists space-separated paths on the target to retrieve onto
the host, when inheriting testimage.

(From yocto-docs rev: 2537642d2cdf844dc5f6027fb3097aac52162c1f)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/variables.rst

@@ -9267,6 +9267,11 @@ system and gives an overview of their function and contents.
       section in the Yocto Project Development Tasks Manual and the
       ":ref:`ref-classes-testimage`" section.
 
+   :term:`TESTIMAGE_FAILED_QA_ARTIFACTS`
+      When using the :ref:`ref-classes-testimage` class, the variable
+      :term:`TESTIMAGE_FAILED_QA_ARTIFACTS`  lists space-separated paths on the
+      target to retrieve onto the host.
+
    :term:`THISDIR`
       The directory in which the file BitBake is currently parsing is
       located. Do not manually set this variable.