dev-cmd/edit: do not shadow formula with local dir

When current directory contains dir with the same name as formula,
`brew edit <formula>` now opens the formula instead of the dir.

Fixes Homebrew#16015.

Library/Homebrew/cli/named_args.rb

@@ -230,7 +230,7 @@ def to_paths(only: parent&.only_formula_or_cask, recurse_tap: false)
         @to_paths[only] ||= Homebrew.with_no_api_env_if_needed(@without_api) do
           downcased_unique_named.flat_map do |name|
             path = Pathname(name)
-            if File.exist?(name)
+            if path.file?(name)
               path
             elsif name.count("/") == 1 && !name.start_with?("./", "/")
               tap = Tap.fetch(name)