Rename SqlBufferTests to align with standard

Author: edwardneal

src/Microsoft.Data.SqlClient/tests/UnitTests/Microsoft/Data/SqlClient/SqlBufferTests.cs renamed to src/Microsoft.Data.SqlClient/tests/UnitTests/Microsoft/Data/SqlClient/SqlBufferTest.cs

@@ -16,7 +16,7 @@ namespace Microsoft.Data.SqlClient.UnitTests
     /// Several methods in this class are internal. This is because their parameters are of SqlBuffer.StorageType,
     /// which is non-public.
     /// </remarks>
-    public sealed class SqlBufferTests
+    public sealed class SqlBufferTest
     {
         private readonly SqlBuffer _target = new();