* Sync lockfile from rubygems/rubygems

* Restore lockfile for test-bundler

In the past, bundler updated platform without normalized variable like arm64-darwin-23.
We ignored that update. But the current bundler uses arm64-darwin for that.

---------

Co-authored-by: Hiroshi SHIBATA <hsbt@ruby-lang.org>

https://github.com/ruby/ruby/actions/runs/15199473008/job/42750815986?pr=13421

```
 Error: ArgumentError: wrong number of arguments (given 0, expected 1)
  /Users/runner/work/ruby/ruby/src/lib/rdoc/store.rb:123:in 'initialize'
  /Users/runner/work/ruby/ruby/src/gems/src/rbs/test/rbs/rdoc/rbs_parser_test.rb:8:in 'Class#new'
  /Users/runner/work/ruby/ruby/src/gems/src/rbs/test/rbs/rdoc/rbs_parser_test.rb:8:in 'RDocPluginParserTest#parser'
  /Users/runner/work/ruby/ruby/src/gems/src/rbs/test/rbs/rdoc/rbs_parser_test.rb:147:in 'RDocPluginParserTest#test_instance_method_comment_and_tokens'
```

Previously, the script was caching any file already present in the
destination directory, regardless of its origin. This caused issues
when the directory contained files copied from external sources like
`autoreconf --install`.

For example:
1. `./autogen.sh --install` copies `config.guess` and `config.sub`
   from the system to `./tool`.
2. `ruby tool/downloader.rb -d tool -e gnu config.guess config.sub`
   treats those files as if they were downloaded and caches them.
3. Removing the files: `rm tool/config.guess tool/config.sub`.
4. Running the downloader again, it mistakenly restores the cached
   files instead of downloading fresh versions.