https://github.com/ruby/actions/actions/runs/19420968008/job/55558315338

```
    1) Error:
  TestCommitEmail#test_sendmail_encoding:
  Test::Unit::ProxyError: No such file or directory - git
      /home/runner/work/actions/actions/ruby-4.0.0-preview2/lib/open3.rb:534:in 'Kernel#spawn'
      /home/runner/work/actions/actions/ruby-4.0.0-preview2/lib/open3.rb:534:in 'Open3.popen_run'
      /home/runner/work/actions/actions/ruby-4.0.0-preview2/lib/open3.rb:379:in 'Open3.popen2'
      /home/runner/work/actions/actions/ruby-4.0.0-preview2/lib/open3.rb:785:in 'Open3.capture2'
      /home/runner/work/actions/actions/ruby-4.0.0-preview2/tool/test/test_commit_email.rb:89:in 'TestCommitEmail#git'
      /home/runner/work/actions/actions/ruby-4.0.0-preview2/tool/test/test_commit_email.rb:13:in 'block in TestCommitEmail#setup'
      /home/runner/work/actions/actions/ruby-4.0.0-preview2/tool/test/test_commit_email.rb:12:in 'Dir.chdir'
      /home/runner/work/actions/actions/ruby-4.0.0-preview2/tool/test/test_commit_email.rb:12:in 'TestCommitEmail#setup'

    2) Error:
  TestCommitEmail#test_sendmail_encoding:
  Test::Unit::ProxyError: no implicit conversion of nil into String
      /home/runner/work/actions/actions/ruby-4.0.0-preview2/tool/test/test_commit_email.rb:37:in 'File.unlink'
      /home/runner/work/actions/actions/ruby-4.0.0-preview2/tool/test/test_commit_email.rb:37:in 'TestCommitEmail#teardown'
```

When there are nested capture variables inside of a pattern match
that has an alternation pattern, it is a syntax error. Currently it
only adds a syntax error when it is at the top level of the pattern.