<fix>[driver]:csharp change close() return type to void (#11340)

src/connector/C#/examples/lib/Utils.cs

@@ -161,14 +161,12 @@ namespace Sample.UtilsTools
             ExecuteUpdate(conn, $"drop database if  exists {globalDbName}");
             if (conn != IntPtr.Zero)
             {
-                if (TDengine.Close(conn) == 0)
-                {
+                TDengine.Close(conn);
                 Console.WriteLine("close connection success");
             }
             else
             {
-                    Console.WriteLine("close Connection failed");
-                }
+                throw new Exception("connection if already null");
             }
         }
         public static List<TDengineMeta> GetResField(IntPtr res)

src/connector/C#/src/TDengineDriver/TDengineDriver.cs

@@ -280,7 +280,7 @@ namespace TDengineDriver
         static extern public IntPtr FreeResult(IntPtr res);
 
         [DllImport("taos", EntryPoint = "taos_close", CallingConvention = CallingConvention.Cdecl)]
-        static extern public int Close(IntPtr taos);
+        static extern public void Close(IntPtr taos);
 
         //get precision of restultset
         [DllImport("taos", EntryPoint = "taos_result_precision", CallingConvention = CallingConvention.Cdecl)]

src/connector/C#/src/test/FunctionTest/lib/DBFixture.cs

@@ -53,14 +53,8 @@ namespace Test.Fixture
                 {
                     if ((res = TDengine.Query(conn, $"drop database if exists {db}")) != IntPtr.Zero)
                     {
-                        if (TDengine.Close(conn) == 0)
-                        {
+                        TDengine.Close(conn);
                         Console.WriteLine("close connection success");
-                        }
-                        else
-                        {
-                            throw new Exception("close connection failed");
-                        }
    
                     }
                     else

src/connector/C#/src/test/FunctionTest/lib/Utils.cs

@@ -158,14 +158,12 @@ namespace Test.UtilsTools
             ExecuteUpdate(conn, "drop database if  exists csharp");
             if (conn != IntPtr.Zero)
             {
-                if (TDengine.Close(conn) == 0)
-                {
+                TDengine.Close(conn);
                 Console.WriteLine("close connection success");
             }
             else
             {
-                    Console.WriteLine("close Connection failed");
-                }
+                 throw new Exception("connection if already null");
             }
         }
         public static List<TDengineMeta> GetResField(IntPtr res)