Unexcepted additional .git keyword in XCRemoteSwiftPackageReference

Xcodeproj version: `1.20.0`
I want to update the version of a swift package. Hence I emulated the objects and found the package. Then I modified the version and saved it. But I couldn't open my Xcode project. It seems my `.pbxproj` format is incorrect.

Here is my code:
``` ruby
project_path = './myproject.xcodeproj'

if !File.exist?(project_path)
print "Didn't find .xcodeproj file at '#{project_path}'\n"
exit(1)
end

project = Xcodeproj::Project.open(project_path)

project.objects.each do |object|
next unless 'some_package' == object.display_name && object.is_a?(Xcodeproj::Project::Object::XCSwiftPackageProductDependency)
object.package.requirement["version"] = '456'
print "display_name: #{object.display_name}, requirement: #{object.package.requirement["version"]}\n"
end

project.save
```

Reproduce the problem with the Ruby script in the issue, using Xcodeproj 1.20.0 and an Xcode project containing the affected Swift package reference. Inspect how XCRemoteSwiftPackageReference objects are serialized during project.save; done means the saved .pbxproj no longer contains the unexpected additional .git keyword and opens in Xcode.

Written by the indexing model from the issue text.