Extend expiry dates for IsolatableSandboxedIframes metrics.

This CL extends the expiry dates for both

SiteIsolation.IsolatableSandboxedIframes.UniqueOrigin and
SiteIsolation.IsolatableSandboxedIframes.UniqueSites

and makes them match the expiry date for

SiteIsolation.IsolatableSandboxedIframes

All these metrics are still in use.

Bug: 400444617
Change-Id: Idc6ac174eb8f8b2ce8b2fb09d3afb890aba4b01b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6437922
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: James Maclean <wjmaclean@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1444219}