[release/10.0.1xx] Add .slnx to default .editorconfig template (#51095)

Author: marcpopMSFT

template_feed/Microsoft.DotNet.Common.ItemTemplates/content/EditorConfig/Dotnet/.editorconfig

@@ -9,7 +9,7 @@ indent_style = space
 indent_size = 2
 
 # Xml project files
-[*.{csproj,fsproj,vbproj,proj}]
+[*.{csproj,fsproj,vbproj,proj,slnx}]
 indent_size = 2
 
 # Xml config files

test/dotnet-new.IntegrationTests/Approvals/AllCommonItemsCreate.-o#EditorConfig-file#-n#item.verified/EditorConfig-file/.editorconfig

@@ -9,7 +9,7 @@ indent_style = space
 indent_size = 2
 
 # Xml project files
-[*.{csproj,fsproj,vbproj,proj}]
+[*.{csproj,fsproj,vbproj,proj,slnx}]
 indent_size = 2
 
 # Xml config files