CICD: fix upload and make e2e_subs_nightly required

[onetechnical]

Summary

For GitHub Actions, a rebuild before upload is required to install all the relevant files. However, explicitly for Linux nightly builds, these were skipped, which broke the upload step.

This PR also makes the following additional changes:

• makes e2e_subs_nightly explicitly required - tests would pass if other validations passed, but these failed
• Add support for passing S3_TESTDATA as a custom S3 bucket

Test Plan

Testing on a fork to verify, but all steps should pass with the next rel/nightly merge.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 50.45%. Comparing base (981d065) to head (757699c).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6369      +/-   ##
==========================================
+ Coverage   48.57%   50.45%   +1.87%     
==========================================
  Files         653      653              
  Lines      110395   110395              
==========================================
+ Hits        53621    55696    +2075     
+ Misses      53842    51837    -2005     
+ Partials     2932     2862      -70     

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