[resign] fix incorrectly typoed variable name

[silvervest]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

As @kapfab found in #18713 (comment), a previous variable name was incorrectly set when fixing a merge conflict. This resolves that.

Description

Changing the variable from $CERTIFICATE to the local $certificate_name to ensure the correct environment is used when processing iCloud Environment keys

Testing Steps

[silvervest]

@joshdholtz apologies to bug you, this is a fix for an error in my PR you merged earlier today that could affect some distribution resigning. It would be good to merge at the same time to avoid issues! Thanks again!

[joshdholtz]

Thanks for following up so quickly on this! 😊

[fastlane-bot]

Hey @silvervest 👋

Thank you for your contribution to fastlane and congrats on getting this pull request merged 🎉
The code change now lives in the master branch, however it wasn't released to RubyGems yet.
We usually ship about once a week, and your PR will be included in the next one.

Please let us know if this change requires an immediate release by adding a comment here 👍
We'll notify you once we shipped a new release with your changes 🚀

[fastlane-bot]

Congratulations! 🎉 This was released as part of fastlane 2.184.0 🚀