Merge bitcoin/bitcoin#29459: test: check_mempool_result negative feerate

bf264e0 test: check_mempool_result negative feerate (kevkevin)

Pull request description:

  Adds test coverage in `mempool_accept.py` to check if a negative `maxfeerate` is input into `check_mempool_result`
  Asserts "Amount out of range" error message and `-3` error code

  Motivated by this [comment](https://github.com/bitcoin/bitcoin/pull/29434/files#r1491112250)

ACKs for top commit:
  maflcko:
    lgtm ACK bf264e0
  brunoerg:
    nice, utACK bf264e0
  davidgumberg:
    Looks great, ACK bitcoin/bitcoin@bf264e0

Tree-SHA512: 58931b774cc887c616f2fd91af3ee65cc5db55acd8e2875c76de448c80bd4e020b057c5f4f85556431377f0d0e7553771fb285d1ec20cf64f64ec92a47776b78

Author: glozow

test/functional/mempool_accept.py

@@ -96,6 +96,12 @@ def run_test(self):
             rawtxs=[raw_tx_in_block],
             maxfeerate=1,
         ))
+        # Check negative feerate
+        assert_raises_rpc_error(-3, "Amount out of range", lambda: self.check_mempool_result(
+            result_expected=None,
+            rawtxs=[raw_tx_in_block],
+            maxfeerate=-0.01,
+        ))
         # ... 0.99 passes
         self.check_mempool_result(
             result_expected=[{'txid': txid_in_block, 'allowed': False, 'reject-reason': 'txn-already-known'}],