Update writing-tests-cosmwasm.mdx

Author: Bilogweb3

src/pages/cw-multi-test/getting-started/writing-tests/writing-tests-cosmwasm.mdx

@@ -1138,7 +1138,7 @@ Nice, you have reached 💯% code coverage.
  }
 ```
 
-All functionalities of the **counter** smart contract has been tested, the code coverage report
+All functionalities of the **counter** smart contract have been tested, the code coverage report
 `shines green{:ansi}`.
 
 ## Test cases put all together