Add sync_blocks in wallet_orphanedreward.py.

Add an explicit sync_blocks call in wallet_orphanedreward.py, which was
missing and could lead to intermittent failures of the test due to
race conditions.

This will presumably fix bitcoin#22181.

test/functional/wallet_orphanedreward.py

@@ -31,6 +31,7 @@ def run_test(self):
         # Let the block reward mature and send coins including both
         # the existing balance and the block reward.
         self.nodes[0].generate(150)
+        self.sync_blocks()
         assert_equal(self.nodes[1].getbalance(), 10 + 25)
         txid = self.nodes[1].sendtoaddress(self.nodes[0].getnewaddress(), 30)