Merge bitcoin#26941: test: Fix intermittent feature_rbf issue

fa88c04 test: Fix intermittent feature_rbf issue (MarcoFalke)

Pull request description:

  The miniwallet will rescan the chain and mempool on construction. If the mempools are still in sync, it may lead to crashes. Fix that by moving the sync first.

  Fixes bitcoin#26937

ACKs for top commit:
  theStack:
    Code-review ACK fa88c04

Tree-SHA512: 5ffcd5e91118b57811b62f12454da8ae3ca98ffad175cd895cd41b63d7cf420906b1e15a4d4489d223d6b21ab796f9839676af8a5f340c606868bc249f4ea340

Author: fanquake

test/functional/feature_rbf.py

@@ -392,11 +392,11 @@ def test_too_many_replacements_with_default_mempool_params(self):
         enough transactions off of each root UTXO to exceed the MAX_REPLACEMENT_LIMIT.
         Then create a conflicting RBF replacement transaction.
         """
-        normal_node = self.nodes[1]
-        wallet = MiniWallet(normal_node)
         # Clear mempools to avoid cross-node sync failure.
         for node in self.nodes:
             self.generate(node, 1)
+        normal_node = self.nodes[1]
+        wallet = MiniWallet(normal_node)
 
         # This has to be chosen so that the total number of transactions can exceed
         # MAX_REPLACEMENT_LIMIT without having any one tx graph run into the descendant