Update test configuration to vendorize dandiapi instance used in tests

[candleindark]

This PR updates test configuration in a GH workflow to vendorize the dandiapi instance used in tests. It builds on dandi/dandi-cli#1756, so it only works property after dandi/dandi-cli#1756 is merged.

This PR closes #350.

Notes:

• 1. For this PR to have any effect, Make dandi-archive instance used by tests vendorizable dandi-cli#1756 must be merged.
• 2. After Make dandi-archive instance used by tests vendorizable dandi-cli#1756 is merged, this PR is expected to fail until all more vendorization efforts for dandi-cli, , such as Review operation and codebase for further hardcoded DANDI identifiers dandi-cli#1752, are complete.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.89%. Comparing base (58ccbca) to head (18fae25).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #355   +/-   ##
=======================================
  Coverage   97.89%   97.89%           
=======================================
  Files          18       18           
  Lines        2377     2377           
=======================================
  Hits         2327     2327           
  Misses         50       50           

Flag	Coverage Δ
unittests	97.89% <ø> (ø)

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.

[Copilot]

Pull request overview

This PR updates the GitHub Actions test workflow to support vendorized dandiapi instances in tests. It adds matrix configuration for testing against the ember-dandi instance with specific instance metadata (name, identifier, DOI prefix).

Key changes:

• Adds vendored_dandiapi matrix dimension with "default" option
• Introduces two new test matrix combinations for ember-dandi with both master and release versions
• Conditionally sets environment variables for instance configuration

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review for a chance to win a $100 gift card. Take the survey.

[yarikoptic]

@candleindark note that we got conflicts now

[candleindark]

@yarikoptic I accidentally deleted the wrong branch because I mixed this branch with the one I created for dandi/dandi-cli#1771.

I will create another PR.

[yarikoptic]

there is "Restore branch" button I see which I guess could have just been pressed?

[candleindark]

there is "Restore branch" button I see which I guess could have just been pressed?

I don't see that button. I deleted the branch as a remote branch via terminal.

[candleindark]

testing