ci: Error if no files found when uploading source artifacts

[FrederikBolding]

We don't want to proceed with the next CI tasks if we cannot upload the artifacts required for them.

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Note

Medium Risk
Tightens CI/release behavior by failing jobs when expected artifacts aren’t produced, which could surface previously hidden build issues and block downstream steps.

Overview
Ensures CI stops early if required build outputs aren’t present by setting if-no-files-found: error on key actions/upload-artifact steps.

This makes the build-lint-test workflow fail when it can’t upload the snaps-execution-environments build or overall build-source artifacts, and makes publish-release fail if release build artifacts aren’t generated.

^{Reviewed by Cursor Bugbot for commit 1b68b38. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.47%. Comparing base (c339e31) to head (1b68b38).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3958      +/-   ##
==========================================
+ Coverage   98.56%   99.47%   +0.90%     
==========================================
  Files         428      261     -167     
  Lines       12348     7446    -4902     
  Branches     1939     1143     -796     
==========================================
- Hits        12171     7407    -4764     
+ Misses        177       39     -138     

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