Disable flaky test: OSSettingsCrostiniPageTest.All

TBR=nverne@chromium.org, jamescook@chromium.org

No-Try: true
Bug: 1056268
Change-Id: Ibdd6e0b9321301f53ab2fcb451740776c629d232
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2084189
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746224}

chrome/test/data/webui/settings/chromeos/os_settings_browsertest.js

@@ -454,7 +454,8 @@ var OSSettingsCrostiniPageTest = class extends OSSettingsBrowserTest {
   }
 };
 
-TEST_F('OSSettingsCrostiniPageTest', 'All', () => {
+// Disabled due to flakiness: https://crbug.com/1056268.
+TEST_F('OSSettingsCrostiniPageTest', 'DISABLED_All', () => {
   mocha.run();
 });