Fix Map::set owned args and remove unused String import in test

Author: Ce-Royals

contracts/invoice/src/lib.rs

@@ -930,7 +930,7 @@ impl InvoiceContract {
         for status in statuses {
             let key = String::from_str(&env, status.as_str());
             let value = read_status_count(&env, status);
-            counts.set(&key, &value);
+            counts.set(key, value);
         }
         counts
     }

contracts/invoice/src/test.rs

@@ -5,7 +5,7 @@ use proptest::test_runner::{Config as ProptestConfig, TestRunner};
 use soroban_sdk::{
     contract, contractimpl, contracttype,
     testutils::{Address as _, Events as _, Ledger},
-    vec, Address, BytesN, Env, IntoVal, String, Symbol,
+    vec, Address, BytesN, Env, IntoVal, Symbol,
 };
 
 use crate::{InvoiceContract, InvoiceContractClient, InvoiceStatus};