doc: Fix getmempoolancestor RPC result doc
doc: Fix getmempoolancestor RPC result doc

Summary: This is a backport of [[https://github.com/bitcoin/bitcoin/pull/19765 | core#19765]]

Test Plan:
Run this command before and after the change:
```
src/bitcoin-cli help getmempoolancestors > before.txt
```

Compare:
```
$ git diff --ignore-all-space  ~/before.txt ~/after.txt
diff --git a/home/pierre/before.txt b/home/pierre/after.txt
index b241d3c9e9..343a383459 100644
--- a/home/pierre/before.txt
+++ b/home/pierre/after.txt
@@ -14,6 +14,7 @@ Result (for verbose = false):

 Result (for verbose = true):
 {                                  (json object)
+  "transactionid" : {              (json object)
     "size" : n,                    (numeric) transaction size.
     "fee" : n,                     (numeric) transaction fee in XEC (DEPRECATED)
     "modifiedfee" : n,             (numeric) transaction fee with fee deltas used for mining priority (DEPRECATED)
@@ -40,6 +41,8 @@ Result (for verbose = true):
       ...
     ],
     "unbroadcast" : true|false     (boolean) Whether this transaction is currently unbroadcast (initial broadcast not yet acknowledged by any peers)
+  },
+  ...
 }

 Examples:
```

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10115

Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc