Fix warnings for exceptions

Author: christophwille

ICSharpCode.AvalonEdit/Editing/DragDropException.cs

@@ -50,12 +50,13 @@ public DragDropException(string message) : base(message)
 		public DragDropException(string message, Exception innerException) : base(message, innerException)
 		{
 		}
-
+#if !NET6_0_OR_GREATER
 		/// <summary>
 		/// Deserializes a DragDropException.
 		/// </summary>
 		protected DragDropException(SerializationInfo info, StreamingContext context) : base(info, context)
 		{
 		}
+#endif
 	}
 }

ICSharpCode.AvalonEdit/Highlighting/HighlightingDefinitionInvalidException.cs

@@ -47,12 +47,13 @@ public HighlightingDefinitionInvalidException(string message) : base(message)
 		public HighlightingDefinitionInvalidException(string message, Exception innerException) : base(message, innerException)
 		{
 		}
-
+#if !NET6_0_OR_GREATER
 		/// <summary>
 		/// Creates a new HighlightingDefinitionInvalidException instance.
 		/// </summary>
 		protected HighlightingDefinitionInvalidException(SerializationInfo info, StreamingContext context) : base(info, context)
 		{
 		}
+#endif
 	}
 }

ICSharpCode.AvalonEdit/Rendering/VisualLinesInvalidException.cs

@@ -48,12 +48,13 @@ public VisualLinesInvalidException(string message) : base(message)
 		public VisualLinesInvalidException(string message, Exception innerException) : base(message, innerException)
 		{
 		}
-
+#if !NET6_0_OR_GREATER
 		/// <summary>
 		/// Creates a new VisualLinesInvalidException instance.
 		/// </summary>
 		protected VisualLinesInvalidException(SerializationInfo info, StreamingContext context) : base(info, context)
 		{
 		}
+#endif
 	}
 }

ICSharpCode.AvalonEdit/Search/ISearchStrategy.cs

@@ -93,11 +93,12 @@ public SearchPatternException(string message) : base(message)
 		public SearchPatternException(string message, Exception innerException) : base(message, innerException)
 		{
 		}
-
+#if !NET6_0_OR_GREATER
 		// This constructor is needed for serialization.
 		/// <inheritdoc/>
 		protected SearchPatternException(SerializationInfo info, StreamingContext context) : base(info, context)
 		{
 		}
+#endif
 	}
 }