tests: Disable 2 core Timing MESI_Two_Level X86 boot test

This is due to this error: https://gem5.atlassian.net/browse/GEM5-1219.
After several weeks of failing Weekly tests, this test will be disabled
until it can be fixed.

Change-Id: If7510426c33f3412a559681f653e955409fcdce4
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/59329
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>

tests/gem5/x86-boot-tests/test_linux_boot.py

@@ -282,7 +282,8 @@ run_map = {
         },
         "timing": {
             1: True,
-            2: True,
+            2: False,  # Disabled due to
+                       # https://gem5.atlassian.net/browse/GEM5-1219.
             4: True,
             8: True,
         },