Change ReSharper C# language version to 7.3

Author: mdonatas

GitExtensions.sln.DotSettings

@@ -1,5 +1,5 @@
 <wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
-	<s:String x:Key="/Default/CodeInspection/CSharpLanguageProject/LanguageLevel/@EntryValue">CSharp72</s:String></wpf:ResourceDictionary>
+	<s:String x:Key="/Default/CodeInspection/CSharpLanguageProject/LanguageLevel/@EntryValue">CSharp73</s:String></wpf:ResourceDictionary>
 	<s:String x:Key="/Default/CodeInspection/Highlighting/InspectionSeverities/=ConvertClosureToMethodGroup/@EntryIndexedValue">HINT</s:String>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_ACCESSORHOLDER_ATTRIBUTE_ON_SAME_LINE_EX/@EntryValue">NEVER</s:String>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_WHILE_ON_NEW_LINE/@EntryValue">True</s:Boolean>