Fix grammar in exception message.

Author: bgrainger

src/MySqlConnector/MySqlBulkCopy.cs

@@ -347,7 +347,7 @@ private async ValueTask<MySqlBulkCopyResult> WriteToServerAsync(IOBehavior ioBeh
 		if (!m_wasAborted && rowsInserted != m_rowsCopied)
 		{
 			Log.Error("Bulk copy to DestinationTableName={0} failed; RowsCopied={1}; RowsInserted={2}", tableName, m_rowsCopied, rowsInserted);
-			throw new MySqlException(MySqlErrorCode.BulkCopyFailed, "{0} rows were copied to {1} but only {2} were inserted.".FormatInvariant(m_rowsCopied, tableName, rowsInserted));
+			throw new MySqlException(MySqlErrorCode.BulkCopyFailed, "{0} rows {1} copied to {2} but only {3} {4} inserted.".FormatInvariant(m_rowsCopied, m_rowsCopied == 1 ? "was" : "were", tableName, rowsInserted, rowsInserted == 1 ? "was" : "were"));
 		}
 
 		return new(errors, rowsInserted);