test: fix intermittent failure in wallet_resendwallettransactions.py #28108

<details><summary>Some doc and logging ideas after a cursory look, feel free to ignore</summary><p>

@@ -109,21 +109,22 @@ class ResendWalletTransactionsTest(BitcoinTestFramework):
         node.syncwithvalidationinterfacequeue()
 
         evict_time = block_time + 60 * 60 * DEFAULT_MEMPOOL_EXPIRY_HOURS + 5
-        # Flush out currently scheduled resubmit attempt now so that there can't be one right between eviction and check.
+
+        self.log.info("Flush out currently scheduled resubmit attempt now so there cannot be one between eviction and check")
         with node.assert_debug_log(['resubmit 2 unconfirmed transactions']):
             node.setmocktime(evict_time)
-            node.mockscheduler(60)
+            node.mockscheduler(60)  # Tell scheduler to call MaybeResendWalletTxs now
 
-        # Evict these txs from the mempool
+        self.log.info("Evict these txs from the mempool")
         indep_send = node.send(outputs=[{node.getnewaddress(): 1}], inputs=[indep_utxo])
         node.getmempoolentry(indep_send["txid"])
         assert_raises_rpc_error(-5, "Transaction not in mempool", node.getmempoolentry, txid)
         assert_raises_rpc_error(-5, "Transaction not in mempool", node.getmempoolentry, child_txid)
 
-        # Rebroadcast and check that parent and child are both in the mempool
+        self.log.info("Rebroadcast and check that parent and child are both in the mempool")
         with node.assert_debug_log(['resubmit 2 unconfirmed transactions']):
             node.setmocktime(evict_time + 36 * 60 * 60) # 36 hrs is the upper limit of the resend timer
-            node.mockscheduler(60)
+            node.mockscheduler(60)  # Tell scheduler to call MaybeResendWalletTxs now
         node.getmempoolentry(txid)
         node.getmempoolentry(child_txid)

</p></details>

Generally I am not really a fan of using assert_debug_log to sync. If you do, my preference would be to use the timeout argument. Even better would be to sync inside the body. Either with a call to syncwithvalidationinterfaceque or by modifying the RPC:

diff --git a/src/rpc/node.cpp b/src/rpc/node.cpp
index 3828401642..f614253195 100644
--- a/src/rpc/node.cpp
+++ b/src/rpc/node.cpp
@@ -93,6 +93,7 @@ static RPCHelpMan mockscheduler()
     // protect against null pointer dereference
     CHECK_NONFATAL(node_context->scheduler);
     node_context->scheduler->MockForward(std::chrono::seconds(delta_seconds));
+    SyncWithValidationInterfaceQueue();
 
     return UniValue::VNULL;
 },

Otherwise, if someone removes the log, the test may fail again if the scheduler queue has several entries.

Attempt in https://github.com/bitcoin/bitcoin/pull/28118