wallet, bugfix: allow send to take string fee rate values

src/wallet/rpcwallet.cpp

@@ -4089,7 +4089,7 @@ static RPCHelpMan send()
                 UniValueType(), // outputs (ARR or OBJ, checked later)
                 UniValue::VNUM, // conf_target
                 UniValue::VSTR, // estimate_mode
-                UniValue::VNUM, // fee_rate
+                UniValueType(), // fee_rate, will be checked by AmountFromValue() in SetFeeEstimateMode()
                 UniValue::VOBJ, // options
                 }, true
             );

test/functional/wallet_send.py

@@ -256,8 +256,8 @@ class WalletSendTest(BitcoinTestFramework):
         assert res["complete"]
 
         self.log.info("Test setting explicit fee rate")
-        res1 = self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_fee_rate=1, add_to_wallet=False)
-        res2 = self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate=1, add_to_wallet=False)
+        res1 = self.test_send(from_wallet=w0, to_wallet=w1, amount=1, arg_fee_rate="1", add_to_wallet=False)
+        res2 = self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate="1", add_to_wallet=False)
         assert_equal(self.nodes[1].decodepsbt(res1["psbt"])["fee"], self.nodes[1].decodepsbt(res2["psbt"])["fee"])
 
         res = self.test_send(from_wallet=w0, to_wallet=w1, amount=1, fee_rate=7, add_to_wallet=False)