tests: try to reduce flakyness of test_fail_pending_htlcs_on_shutdown

Alice sends and HTLC: Alice->Carol->Dave
we need a lot of messages back and forth to happen:
- Alice adds HTLC to chan_AC, sends sig, Carol revacks, sends sig, Alice revacks;
- only then Carol adds HTLC to chan_CD, sends sig, Dave revacks, sends sig, Carol revacks
on CI, 0.5 seconds is often not enough for this it seems.

electrum/tests/test_lnpeer.py

@@ -970,7 +970,7 @@ class TestPeer(TestCaseForTestnet):
             assert graph.w_a.network.channel_db is not None
             lnaddr, pay_req = await self.prepare_invoice(graph.w_d, include_routing_hints=True, amount_msat=amount_to_pay)
             try:
-                async with timeout_after(0.5):
+                async with timeout_after(1.0):
                     result, log = await graph.w_a.pay_invoice(pay_req, attempts=1)
             except TaskTimeout:
                 # by now Dave hopefully received some HTLCs: