Replace removed File.exists? with File.exist? for Ruby 3.2.0 compatibility

[umihico]

Brief Summary of Changes

This update replaces the deprecated and removed File.exists? method with File.exist? to ensure compatibility with Ruby 3.2.0 and later versions, where the old method has been entirely removed.

https://www.ruby-lang.org/en/news/2022/12/25/ruby-3-2-0-released/

What does this PR address?

• [ ] GitHub issue (Add reference - #XX)
• [ ] Refactoring
• [ ] New feature
• [x] Bug fix
• [ ] Adds more tests

Are tests included?

• [ ] Yes
• [x] No

Reviewer, please note:

I am not sure the function cl_sprite_url is still in use.

Checklist:

• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I ran the full test suite before pushing the changes and all the tests pass.

[const-cloudinary]

@umihico thank you for contribution!