fix: .gitignore copied to build folder

[labrom]

Description

When running the dart_frog build command, the .gitignore file that exists at the root of my project is copied over to the build folder.

Steps To Reproduce

1. Initialize git in the project, check that the .gitignore file exists at the root of the project
2. Run dart_frog build
3. Check the presence of the .gitignore file in the build folder

Expected Behavior

This git file shouldn't be copied to the build folder, there should only be one in the root directory of the project.

[AliYar-Khan]

seems like a bug in mason generator