Disable discourse_infinite_scroll:2018 on Win7

This is frequently failing on win7 bots.

TBR=johnchen@chromium.org

Bug: 1088447
Change-Id: Ia1b3778647f01afce6349cab31fedb8a2933713c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225367Reviewed-by: Thomas Guilbert <tguilbert@chromium.org>
Commit-Queue: Thomas Guilbert <tguilbert@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773873}

tools/perf/expectations.config

@@ -335,6 +335,7 @@ crbug.com/934885 [ linux ] system_health.memory_desktop/load_accessibility:media
 crbug.com/869118 [ linux ] system_health.memory_desktop/long_running:tools:gmail-background [ Skip ]
 crbug.com/899887 [ linux ] system_health.memory_desktop/browse:social:facebook_infinite_scroll:2018 [ Skip ]
 crbug.com/924330 [ linux ] system_health.memory_desktop/browse:media:pinterest:2018 [ Skip ]
+crbug.com/1088447 [ win7 ] system_health.memory_desktop/browse:tech:discourse_infinite_scroll:2018 [ Skip ]
 crbug.com/874803 [ win10 ] system_health.memory_desktop/multitab:misc:typical24 [ Skip ]
 crbug.com/944978 [ win7 ] system_health.memory_desktop/multitab:misc:typical24 [ Skip ]
 crbug.com/934270 [ win ] system_health.memory_desktop/multitab:misc:typical24:2018 [ Skip ]