Update BasicCoin.move

Fix warnings
```
warning[W10007]: potential issue with attribute value
   ┌─ ./sources/BasicCoin.move:94:24
   │
94 │     #[expected_failure(abort_code = 2)] // Can specify an abort code
   │                        ^^^^^^^^^^   - Replace value with constant from expected module or add `location=...` attribute.
   │                        │             
   │                        WARNING: passes for an abort from any module.
```

language/documentation/tutorial/step_5/BasicCoin/sources/BasicCoin.move

@@ -91,7 +91,7 @@ module NamedAddr::BasicCoin {
     }
 
     #[test(account = @0x1)]
-    #[expected_failure(abort_code = 2)] // Can specify an abort code
+    #[expected_failure(abort_code = EALREADY_HAS_BALANCE)] // Can specify an abort code
     fun publish_balance_already_exists(account: signer) {
         publish_balance(&account);
         publish_balance(&account);