Remove accidentally added nuget.exe and update .gitignore

Co-authored-by: christianhelle <710400+christianhelle@users.noreply.github.com>

Author: Copilot

.gitignore

@@ -187,6 +187,8 @@ PublishScripts/
 # NuGet v3's project.json files produces more ignorable files
 *.nuget.props
 *.nuget.targets
+# NuGet executable
+.nuget/nuget.exe
 
 # Microsoft Azure Build Output
 csx/