fix(security): resolve CodeQL warnings

[Nuzair46]

Fixed codeql security warnings:

• https://github.com/rubyconfig/config/security/code-scanning/6
• https://github.com/rubyconfig/config/security/code-scanning/5

[Copilot]

Pull Request Overview

Fix CodeQL security warnings by replacing regex patterns with safer, clearer alternatives.

• Replace a complex regex in method_missing with String#end_with? to detect setter methods.
• Update the environment parser regex to use an atomic grouping to prevent backtracking.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lib/config/options.rb	Swapped regex check for setter methods with method_name.to_s.end_with?('=').
lib/config/integrations/heroku.rb	Changed the trailing-word regex to use an atomic group (?>\w+) instead of (\w+).

Comments suppressed due to low confidence (2)

lib/config/options.rb:153

• Consider adding unit tests for missing setter methods to ensure fail_on_missing is correctly bypassed for setter calls and raises a KeyError for undefined getters.

      if Config.fail_on_missing && !method_name.to_s.end_with?('=')

lib/config/integrations/heroku.rb:29

• [nitpick] Add a brief comment explaining the use of the atomic grouping (?>\w+) to clarify that it prevents regex backtracking and addresses the CodeQL warning.

        heroku("run 'echo $RAILS_ENV'").chomp[/(?>\w+)\z/]