Improvements to test-go CI job

[getvictor]

This PR makes several improvements to test-go CI job

• remove ZSH dependency from all test suites except for a new scripts suite
• add a fast suite that does not have out-of-process dependencies, which completes in ~1.5 minutes
  • contributors can add their fast tests to this suite so they can see the results in CI faster
• Rename core to main test suite to be consistent with Makefile. It is the default bucket for tests.
• Cleaned up Makefile so that it is more straightforward to add new test suites or move Go packages between suites
• Do not stop the test suites on a fail.
  • We do not want to be blocked by a test fail that another product team introduced
  • Sometimes, we want to see all test failures so we can fix them all at once.
• Removed test-schema and mock prerequisites for test-go since they are not needed and just take up time.
  • But also added test-schema run to one of the test suites just in case.

Unfortunately, fleetctl is still the bottleneck and needs to be refactored. New issue filed: #27927

Before

After

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.88%. Comparing base (45fe5b2) to head (6811ca0).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #27916      +/-   ##
==========================================
+ Coverage   63.67%   63.88%   +0.21%     
==========================================
  Files        1775     1772       -3     
  Lines      169498   169470      -28     
  Branches     4947     4834     -113     
==========================================
+ Hits       107928   108267     +339     
+ Misses      53137    52666     -471     
- Partials     8433     8537     +104     

Flag	Coverage Δ
backend	64.96% <ø> (+0.22%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.