Merge bitcoin/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 #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