[RHELC-1535] Test set envar through config

[danmyway]

• modify one of the tests to validate the functionality

Jira Issues:

• RHELC-1535

Checklist

• [x] PR has been tested manually in a VM (either author or reviewer)
• [x] Jira issue has been made public if possible
• [x] [RHELC-] or [HMS-] is part of the PR title
• [x] Label depicting the kind of PR it is
• [x] PR title explains the change from the user's point of view
• [x] Code and tests are documented properly
• [x] The commits are squashed to as few commits as possible (without losing data)
• [ ] When merged: Jira issue has been updated to Release Pending if relevant

[has-bot]

This PR does not require integration tests to be run.

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[danmyway]

/packit test --labels tier1

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.09%. Comparing base (c83d7b6) to head (82584b3). Report is 7 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1440 +/- ## ======================================= Coverage 96.09% 96.09% ======================================= Files 72 72 Lines 5143 5143 Branches 888 888 ======================================= Hits 4942 4942 Misses 119 119 Partials 82 82 ``` | [Flag](https://app.codecov.io/gh/oamg/convert2rhel/pull/1440/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | Coverage Δ | | |---|---|---| | [centos-linux-7](https://app.codecov.io/gh/oamg/convert2rhel/pull/1440/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `91.58% <ø> (ø)` | | | [centos-linux-8](https://app.codecov.io/gh/oamg/convert2rhel/pull/1440/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `92.44% <ø> (ø)` | | | [centos-linux-9](https://app.codecov.io/gh/oamg/convert2rhel/pull/1440/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `92.56% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg#carryforward-flags-in-the-pull-request-comment) to find out more.

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[danmyway]

/packit test --labels tier1