test(app): grow state with fund() instead of pay()

The jtx pay helper is not included in this translation unit (only
Account, Env, amount, envconfig, noop), so pay() was an undeclared
identifier and the build failed. Fund a fresh account each ledger
instead, which this file already uses and which adds new state-map nodes
for each rotation to copy forward.

src/test/app/SHAMapStore_test.cpp

@@ -1077,8 +1077,10 @@ public:
                  ledgerSeq < target;
                  ++ledgerSeq)
             {
-                env(pay(alice, bob, XRP(1)));
-                env(pay(bob, alice, XRP(1)));
+                // A fresh funded account each ledger adds new state-map
+                // nodes, so each rotation copies forward genuinely new data
+                // while alice's and bob's roots persist across the boundary.
+                env.fund(XRP(1000), Account("acct" + std::to_string(ledgerSeq)));
                 env.close();
 
                 auto ledger = env.rpc("ledger", "validated");