[rubygems/rubygems] Stop removing the `.git` folder from cached git gems

If we want to change git gems to use a proper cache, instead of using
the cache folder as the install location, so we need to keep git
information in the cache, so that when running `bundle install` or
`bundler install --local`, we are able to figure out whether the
revision that needs to be checked out is present locally in the cache or
needs to be fetched from the remote repository.

https://github.com/rubygems/rubygems/commit/607eda63eb

lib/bundler/plugin/api/source.rb

@@ -196,6 +196,7 @@ module Bundler
 
           FileUtils.rm_rf(new_cache_path)
           FileUtils.cp_r(install_path, new_cache_path)
+          FileUtils.rm_rf(app_cache_path.join(".git"))
           FileUtils.touch(app_cache_path.join(".bundlecache"))
         end
 

lib/bundler/runtime.rb

@@ -140,7 +140,6 @@ module Bundler
       end
 
       Dir[cache_path.join("*/.git")].each do |git_dir|
-        FileUtils.rm_rf(git_dir)
         FileUtils.touch(File.expand_path("../.bundlecache", git_dir))
       end
 

spec/bundler/cache/git_spec.rb

@@ -25,7 +25,6 @@ RSpec.describe "bundle cache with git" do
     bundle "config set cache_all true"
     bundle :cache
     expect(bundled_app("vendor/cache/foo-1.0-#{ref}")).to exist
-    expect(bundled_app("vendor/cache/foo-1.0-#{ref}/.git")).not_to exist
     expect(bundled_app("vendor/cache/foo-1.0-#{ref}/.bundlecache")).to be_file
 
     FileUtils.rm_rf lib_path("foo-1.0")
@@ -47,7 +46,6 @@ RSpec.describe "bundle cache with git" do
     bundle :cache
 
     expect(bundled_app("vendor/cache/foo-1.0-#{ref}")).to exist
-    expect(bundled_app("vendor/cache/foo-1.0-#{ref}/.git")).not_to exist
 
     FileUtils.rm_rf lib_path("foo-1.0")
     expect(the_bundle).to include_gems "foo 1.0"