refactor: Avoid locking tx pool cs thrice

src/test/policyestimator_tests.cpp

@@ -18,6 +18,7 @@ BOOST_AUTO_TEST_CASE(BlockPolicyEstimates)
 {
     CBlockPolicyEstimator feeEst;
     CTxMemPool mpool(&feeEst);
+    LOCK(mpool.cs);
     TestMemPoolEntryHelper entry;
     CAmount basefee(2000);
     CAmount deltaFee(100);