convert str to float for taking negative

Author: Sha-yol

strategies/sw_balance.py

@@ -25,6 +25,6 @@ def create_transactions(self, exp: Expense, myshare: ExpenseUser, data: list[str
             balance_txn['destination_name'] = paid_txn['destination_name']
             balance_txn['type'] = "withdrawal"
             balance_txn['description'] = f"Balance transfer for: {paid_txn['description']}"
-            balance_txn = self._apply_transaction_amount(balance_txn, exp, -balance)
+            balance_txn = self._apply_transaction_amount(balance_txn, exp, -float(balance))
 
         return [paid_txn, balance_txn]