perf: Disable flaky test: loading.desktop/Kenh14_warm

This test is failing consistently on linux-perf and has already been
disabled on Windows and Mac.

Bug: 1312923
Change-Id: I4cd9ab2aa22bad48eb43d08fe0a0987ac33b5688
NOTRY: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3653404
Auto-Submit: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1005160}

tools/perf/expectations.config

@@ -88,6 +88,7 @@ crbug.com/921428 [ chromeos ] loading.desktop/TheVerge_cold [ Skip ]
 crbug.com/921428 [ chromeos ] loading.desktop/TheVerge_warm [ Skip ]
 crbug.com/1312923 [ win10 ] loading.desktop/Kenh14_warm [ Skip ]
 crbug.com/1312923 [ mac ] loading.desktop/Kenh14_warm [ Skip ]
+crbug.com/1312923 [ linux ] loading.desktop/Kenh14_warm [ Skip ]
 
 # Benchmark: loading.mobile
 crbug.com/656861 loading.mobile/G1 [ Skip ]