[Fuchsia] Filter failing accessibility_unittests.

Turn off tests that are failing during investigation.

Bug: 1069808
Change-Id: Id44e389b6be7b96a1cfc1a6543897ee36c5f1506
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2144479Reviewed-by: David Dorwin <ddorwin@chromium.org>
Commit-Queue: Chong Gu <chonggu@google.com>
Cr-Commit-Position: refs/heads/master@{#758256}

testing/buildbot/filters/fuchsia.accessibility_unittests.filter

 # crbug.com/1067395
--AXPlatformNodeBaseTest.InnerTextIgnoresInvisibleAndIgnored
\ No newline at end of file
+-AXPlatformNodeBaseTest.InnerTextIgnoresInvisibleAndIgnored
+
+# crbug.com/1069808
+-AXPlatformNodeBaseTest.TestSelectedChildren*
\ No newline at end of file