Use Digest::MD5.file instead of Digest::MD5.hexdigest

[reflexing]

Fixes #20527

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 see several green ci/circleci builds in the "All checks have passed" section of my PR (connect CircleCI to GitHub if not)
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.
• I've added or updated relevant unit tests.

Motivation and Context

fastlane fails to upload large .pkg and crashes. I know nothing about Ruby, but apparently ruby can't handle loading large file at once. MD5.file allows successful package upload.
Resolves #20527

Description

I'm just trying to set up our CI pipeline.

Testing Steps