Fix: add RUSTFLAGS="--cfg vortex_nightly" to all nightly tests

[connortsui20]

I think this is everything, I had claude search through all of our actions

[codecov]

Codecov Report

❌ Patch coverage is 69.69697% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.24%. Comparing base (bf654c4) to head (37852de).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
vortex-compute/src/take/slice/portable.rs	71.87%	18 Missing ⚠️
...rray/src/arrays/primitive/compute/take/portable.rs	0.00%	2 Missing ⚠️

☔ 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.

[a10y]

assuming ci checks pass this seems fine