drm: ci: docs: fix build warning - add missing escape

Fix the following warning:

Documentation/gpu/automated_testing.rst:55: WARNING: Inline emphasis start-string without end-string.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20230824164230.48470-1-helen.koike@collabora.com

Documentation/gpu/automated_testing.rst

@@ -52,7 +52,7 @@ IGT_VERSION
 drivers/gpu/drm/ci/testlist.txt
 -------------------------------
 
-IGT tests to be run on all drivers (unless mentioned in a driver's *-skips.txt
+IGT tests to be run on all drivers (unless mentioned in a driver's \*-skips.txt
 file, see below).
 
 drivers/gpu/drm/ci/${DRIVER_NAME}-${HW_REVISION}-fails.txt