gstreamer1.0: skip another known flaky test

The baseparse:parser_pull_short_read test is known to be unreliable,
according to the list of known bad tests in gst-devtools.

Also clean up an incorrect comment.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>