Disable security.SELinuxFilesSystem tast

Test is flaky.

TBR=oshima@chromium.org

Bug: 1098810
Change-Id: I6cc56badc887f0f7743492b92d0ec705e52fa3b7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2264796Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781939}

chromeos/BUILD.gn

@@ -290,6 +290,9 @@ if (is_chromeos_device) {
 
       # crbug.com/1073084
       "crostini.CopyPaste.wayland_to_x11_artifact",
+
+      # crbug.com/1098810
+      "security.SELinuxFilesSystem",
     ]
   }