Set the expiry of Settings.SafetyCheck.ExtensionsResult to match other SafetyCheck metrics

Bug: 1165183
Change-Id: I6ccea4c08c70dbc77bed222a1a172c6a886f087e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2636155
Auto-Submit: Andrey Zaytsev <andzaytsev@google.com>
Reviewed-by: Martin Šrámek <msramek@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844824}

tools/metrics/histograms/histograms_xml/settings/histograms.xml

@@ -172,7 +172,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Settings.SafetyCheck.ExtensionsResult"
-    enum="SafetyCheckExtensionsStatus" expires_after="M90">
+    enum="SafetyCheckExtensionsStatus" expires_after="2021-06-20">
   <owner>andzaytsev@google.com</owner>
   <owner>msramek@chromium.org</owner>
   <summary>Resulting state of the safety check extensions check.</summary>