fix(testutils): Add missing env var name to RoxPassword error message

[guzalv]

Description

Before:

Messages:       no password set via %s, and could not read password file

After:

Messages:       no password set via ROX_ADMIN_PASSWORD, and could not read password file

User-facing documentation

• CHANGELOG.md is updated OR update is not needed
• documentation PR is created and is linked above OR is not needed

Testing and quality

• the change is production ready: the change is GA, or otherwise the functionality is gated by a feature flag
• CI results are inspected

Automated testing

• added unit tests
• added e2e tests
• added regression tests
• added compatibility tests
• modified existing tests

How I validated my change

CI

[openshift-ci]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
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[github-actions]

🚀 Build Images Ready

Images are ready for commit 17bf2cb. To use with deploy scripts:

export MAIN_IMAGE_TAG=4.11.x-578-g17bf2cb747

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.60%. Comparing base (7678bbc) to head (47e4e72).
⚠️ Report is 9 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #19857   +/-   ##
=======================================
  Coverage   49.60%   49.60%           
=======================================
  Files        2763     2763           
  Lines      208339   208339           
=======================================
  Hits       103342   103342           
  Misses      97332    97332           
  Partials     7665     7665           

Flag	Coverage Δ
go-unit-tests	49.60% <ø> (ø)

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