[Sheriff] Disable flaky MediaFeedsBrowserTest

Tests have been failing flakily but often, starting from:

https://ci.chromium.org/p/chromium/builders/ci/linux-lacros-tester-rel/2384

TBR=beccahughes@chromium.org

Bug: 1124983
Change-Id: I68ed910d8072b5d0298e8e6a84e8b1c60dcc5dec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2421851Reviewed-by: Meredith Lane <meredithl@chromium.org>
Commit-Queue: Meredith Lane <meredithl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809228}

chrome/browser/media/feeds/media_feeds_browsertest.cc

@@ -866,8 +866,9 @@ IN_PROC_BROWSER_TEST_F(MediaFeedsBrowserTest, ResetMediaFeed_OnNavigation) {
   }
 }
 
+// Flaky failures: crbug.com/1124983
 IN_PROC_BROWSER_TEST_F(MediaFeedsBrowserTest,
-                       ResetMediaFeed_OnNavigation_NeverFetched) {
+                       DISABLED_ResetMediaFeed_OnNavigation_NeverFetched) {
   DiscoverFeed(kMediaFeedsTestURL);
 
   ui_test_utils::NavigateToURL(