test: retain the intended behavior of feature_fee_estimation.py nodes

- Increase block weight by 4000 for all nodes with custom -blockmaxweight.
  Prior to this commit, we generated blocks with 4000 weight units less worth of transactions.
  See https://github.com/bitcoin/bitcoin/issues/32461#issuecomment-2925282272 for details.
  This commit fixes it by increasing the block weight by 4000.

test/functional/feature_fee_estimation.py

@@ -146,8 +146,8 @@ class EstimateFeeTest(BitcoinTestFramework):
         self.noban_tx_relay = True
         self.extra_args = [
             [],
-            ["-blockmaxweight=68000"],
-            ["-blockmaxweight=32000"],
+            ["-blockmaxweight=72000"],
+            ["-blockmaxweight=36000"],
         ]
 
     def setup_network(self):