fix: address issue where quota would not correctly track computeclass usage

[tylerslaton]

Part of a fix for https://github.com/acorn-io/manager/issues/2025

This PR fixes an issue where quota would not correctly count "" usage when processing compute classes.

Checklist

• [X] The title of this PR would make a good line in Acorn's Release Note's Changelog
• [X] 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
• [X] All relevant issues are referenced in the PR description. NOTE: don't use GitHub keywords that auto-close issues
• [X] Commits follow contributing guidance
• [X] Automated tests added to cover the changes. If tests couldn't be added, an explanation is provided in the Verification and Testing section
• [X] 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)