[Cookies] Extend TruncatingCharacterInCookieString histogram

Keep this around so we can evaluate the effect of blocking
truncated cookies (which I have a WIP CL for but haven't
submitted for review yet)

Fixed: 1404493
Change-Id: Iab78fca49681d0b98997b6c53379c13554892bbb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4241920
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Mark Pearson <mpearson@chromium.org>
Auto-Submit: Andrew Williams <awillia@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1104257}

tools/metrics/histograms/metadata/cookie/histograms.xml

@@ -795,7 +795,7 @@ chromium-metrics-reviews@google.com.
 </histogram>
 
 <histogram name="Cookie.TruncatingCharacterInCookieString"
-    enum="TruncatingCharacterInCookieStringType" expires_after="2023-02-12">
+    enum="TruncatingCharacterInCookieStringType" expires_after="2023-05-12">
   <owner>bingler@chromium.org</owner>
   <owner>awillia@chromium.org</owner>
   <summary>