[RHELC-1711] Make the initramfs validity check more robust

[danmyway]

• Except the UnicodeDecodeError exception when the initramfs file is badly miscofigured

Jira Issues:

• RHELC-1711

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] GitHub label has been added to help with Release notes
• [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)
• [x] When merged: Jira issue has been updated to Release Pending if relevant

[has-bot]

This PR does not require integration tests to be run.

---

Comment generated by an automation.

Log | Bot Usage

[codecov[bot]]

Codecov Report

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

Project coverage is 96.10%. Comparing base (9c3fabf) to head (39ef291). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1359 +/- ## ======================================= Coverage 96.09% 96.10% ======================================= Files 72 72 Lines 5178 5182 +4 Branches 896 896 ======================================= + Hits 4976 4980 +4 Misses 119 119 Partials 83 83 ``` | [Flag](https://app.codecov.io/gh/oamg/convert2rhel/pull/1359/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/1359/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `91.62% <100.00%> (+<0.01%)` | :arrow_up: | | [centos-linux-8](https://app.codecov.io/gh/oamg/convert2rhel/pull/1359/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `92.47% <100.00%> (+<0.01%)` | :arrow_up: | | [centos-linux-9](https://app.codecov.io/gh/oamg/convert2rhel/pull/1359/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `92.60% <100.00%> (+<0.01%)` | :arrow_up: | 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

[danmyway]

/packit test --labels tier1

[danmyway]

/packit test --labels tier1

[Venefilyn]

@kokesak review and merge when you can