Increase overhead for DMG to 30 megabytes

[tylerslaton]

https://github.com/acorn-io/runtime/actions/runs/5416268615/jobs/9845763422#step:9:787

The size of the DMG was just barely not enough due to compression being slightly different. Adding a larger overhead buffer to ensure this isn't a problem.

Checklist

• The title of this PR would make a good line in Acorn's Release Note's Changelog
• The title of this PR ends with a link to the main issue being address in parentheses, like: This is a title (#1216). Here's an example
• All relevant issues are referenced in the PR description. NOTE: don't use GitHub keywords that auto-close issues
• Commits follow contributing guidance
• Automated tests added to cover the changes. If tests couldn't be added, an explanation is provided in the Verification and Testing section
• Changes to user-facing functionality, API, CLI, and upgrade impacts are clearly called out in PR description
• PR has at least two approvals before merging (or a reasonable exception, like it's just a docs change)