Update Unity.gitignore to add new ignore patterns

Added entries to ignore .slnx files and scene dependency cache.

Unity.gitignore

@@ -43,6 +43,7 @@ ExportedObj/
 *.csproj
 *.unityproj
 *.sln
+*.slnx
 *.suo
 *.tmp
 *.user
@@ -97,3 +98,6 @@ InitTestScene*.unity*
 
 # Auto-generated scenes by play mode tests
 /[Aa]ssets/[Ii]nit[Tt]est[Ss]cene*.unity*
+
+# Auto-generated cache in Assets folder
+/[Aa]ssets/[Ss]ceneDependencyCache*