test: an invite's zone may be EDT or EST, and an unsent install counts from a recent backup (#6355)

The invite test asserted EDT for a time a day from now, so it failed from today:
a one-day link now ends after New York's clocks change on 1 November. It would
have stayed red until March.

The Home Assistant test used a fixed backup time, which put the unsent install
past its deadline at once.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/integration/test_invites.py

@@ -82,7 +82,7 @@ def test_an_invite_is_emailed_and_the_invitee_makes_their_own_account_once(app,
         assert resp.status_code == 302 and resp.headers["Location"].endswith("?done=invited")
         assert len(sent) == 1 and sent[0]["To"] == to
         text = sent[0].get_body(("plain",)).get_content()
-        assert f"{aname} invited you to Steward" in text and "EDT" in text and "UTC" in text
+        assert f"{aname} invited you to Steward" in text and re.search(r"\bE[DS]T\b", text) and "UTC" in text
         key = _KEY.search(text).group(1)
 
         page = await (await admin.get(resp.headers["Location"])).get_data(as_text=True)