extend/kernel: allow exec_editor to open multiple files at once

[bayandin]

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brew edit no longer accepts multiple formula names to open:

$ brew edit vim mc
Error: wrong number of arguments (given 2, expected 1)
/opt/homebrew/Library/Homebrew/vendor/bundle/ruby/3.4.0/gems/sorbet-runtime-0.5.12357/lib/types/private/methods/signature.rb:204:in 'T::Private::Methods::Signature#each_args_value_type'
/opt/homebrew/Library/Homebrew/vendor/bundle/ruby/3.4.0/gems/sorbet-runtime-0.5.12357/lib/types/private/methods/call_validation.rb:227:in 'T::Private::Methods::CallValidation.validate_call'
/opt/homebrew/Library/Homebrew/vendor/bundle/ruby/3.4.0/gems/sorbet-runtime-0.5.12357/lib/types/private/methods/_methods.rb:277:in 'block in Kernel#_on_method_added'
/opt/homebrew/Library/Homebrew/dev-cmd/edit.rb:63:in 'Homebrew::DevCmd::Edit#run'
/opt/homebrew/Library/Homebrew/vendor/bundle/ruby/3.4.0/gems/sorbet-runtime-0.5.12357/lib/types/private/methods/call_validation.rb:282:in 'UnboundMethod#bind_call'
/opt/homebrew/Library/Homebrew/vendor/bundle/ruby/3.4.0/gems/sorbet-runtime-0.5.12357/lib/types/private/methods/call_validation.rb:282:in 'T::Private::Methods::CallValidation.validate_call'
/opt/homebrew/Library/Homebrew/vendor/bundle/ruby/3.4.0/gems/sorbet-runtime-0.5.12357/lib/types/private/methods/_methods.rb:277:in 'block in Homebrew::DevCmd::Edit#_on_method_added'
/opt/homebrew/Library/Homebrew/brew.rb:113:in '<main>'
Please report this issue:
  https://docs.brew.sh/Troubleshooting

Seems to be caused by an unintended change in #20344.
This PR restores the ability of exec_editor to open multiple files at once.

[MikeMcQuaid]

Thanks @bayandin!