Fix gemspec to exclude .gem files from file list

- Added exclusion for .gem files to prevent circular reference error
- Fixes 'contains itself' validation error when building/installing gem

Author: rodrigotoledo

langchainrb_rails.gemspec

@@ -23,7 +23,7 @@ Gem::Specification.new do |spec|
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
   spec.files = Dir.chdir(__dir__) do
     `git ls-files -z`.split("\x0").reject do |f|
-      (f == __FILE__) || f.match(%r{\A(?:(?:bin|test|spec|features)/|\.(?:git|circleci)|appveyor)})
+      (f == __FILE__) || f.match(%r{\A(?:(?:bin|test|spec|features)/|\.(?:git|circleci)|appveyor)}) || f.match?(/\.gem$/)
     end
   end
   spec.bindir = "exe"