If you get the 'Refactoring failed - Files still read-only' as follows:
Please update 'Visual Studio Tools for Git' extension to the latest version (this issue was fixed since version 0.9.5.0 of this addin). You may do that via VS Extension Manager ("Tools | Extensions and Updates").
If the issue is still present after the update, please disable/remove the 'Visual Studio Tools for Git' extension from the Visual Studio.
Please disable embedded GIT provider in Options: Tools | Options | Source Control | Plug-in selection | Select "None";