fix: acceptPropAsAcceptAttr will return extensions properly

[mseyfayi]

What kind of change does this PR introduce?

• Bug Fix
• Feature
• Refactoring
• Style
• Build
• Chore
• Documentation
• CI

Did you add tests for your changes?

• Yes, my code is well tested
• Not relevant

If relevant, did you update the documentation?

• Yes, I've updated the documentation
• Not relevant

Summary
File extensions in the accept property were ignored, for example:

useDropzone({
    accept: {
      'image/jpeg': ['.jpg']
    }
  })

This code was accepting .jfif files too.

Does this PR introduce a breaking change?
Non-breaking change.

Other information

[pushcommit]

Can confirm this. Please approve 🙏 Thanks!

[new20121439]

No one works on this bug fix :)