Allow leverage tier cache to be 4 weeks old.

we've seen from binance that it's not changing this often.

freqtrade/exchange/exchange.py

@@ -2304,7 +2304,7 @@ class Exchange:
             updated = tiers.get('updated')
             if updated:
                 updated_dt = parser.parse(updated)
-                if updated_dt < datetime.now(timezone.utc) - timedelta(days=1):
+                if updated_dt < datetime.now(timezone.utc) - timedelta(weeks=4):
                     logger.info("Cached leverage tiers are outdated. Will update.")
                     return None
             return tiers['data']

tests/exchange/test_okx.py

@@ -472,7 +472,7 @@ def test_load_leverage_tiers_okx(default_conf, mocker, markets, tmpdir, caplog,
 
     api_mock.fetch_market_leverage_tiers.call_count == 0
     # 2 day passes ...
-    time_machine.move_to(datetime.now() + timedelta(days=2))
+    time_machine.move_to(datetime.now() + timedelta(weeks=5))
     exchange.load_leverage_tiers()
 
     assert log_has(logmsg, caplog)