Fix issue installing artifacts from PR builds with multiple runs

[brandond]

Proposed Changes

Fix issue installing artifacts from builds with multiple runs

Also makes error handling and variable capitalization consistent with other functions.

Types of Changes

bugfix

Verification

See linked issue

Testing

Linked Issues

• Install script INSTALL_K3S_PR support does not work if CI has run more than once #10116

User-Facing Change

Further Comments

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 41.81%. Comparing base (1d22b69) to head (34f7636).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10122      +/-   ##
==========================================
- Coverage   47.58%   41.81%   -5.77%     
==========================================
  Files         173      173              
  Lines       14651    14651              
==========================================
- Hits         6972     6127     -845     
- Misses       6348     7361    +1013     
+ Partials     1331     1163     -168     

Flag	Coverage Δ
e2etests	36.44% <ø> (-9.83%)	⬇️
inttests	37.10% <ø> (+17.31%)	⬆️
unittests	11.38% <ø> (ø)

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[manuelbuil]

IIUC, uppercase variables are typically used for env variables. So I think this change is good and makes it closer to bash best practices. Using curly braces, ${var} would even be better I think

[brandond]

no backports, since install script changes only go to master