hbc/locations: arg is file only if absolute or .rb file

Handle the case when an argument passed to `brew cask` is both the name
of a Cask and a non-Cask file in the current working directory.

Fixes https://github.com/caskroom/homebrew-cask/issues/25611.

Library/Homebrew/cask/lib/hbc/locations.rb

@@ -133,9 +133,8 @@ module Hbc
       def path(query)
         query_path = Pathname.new(query)
 
-        if query_path.exist? || query_path.absolute?
-          return query_path
-        end
+        return query_path if query_path.absolute?
+        return query_path if query_path.exist? && query_path.extname == ".rb"
 
         query_without_extension = query.sub(%r{\.rb$}i, "")