fix: lock Sphinx version on CentOS Stream 9

[Venefilyn]

Stream 9 has python v3.9 as the latest version in default stream. You can enable an AppStream to get newer python versions, however that would involve switching out some of the python specific rpms to their pip counterparts, which requires more testing

Jira Issues:

-

Checklist

• [ ] PR has been tested manually in a VM (either author or reviewer)
• [ ] Jira issue has been made public if possible
• [ ] [RHELC-] or [HMS-] is part of the PR title
• [ ] GitHub label has been added to help with Release notes
• [ ] PR title explains the change from the user's point of view
• [ ] Code and tests are documented properly
• [ ] 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

[codecov[bot]]

Codecov Report

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

Project coverage is 96.52%. Comparing base (f94ddd5) to head (c912fef). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1345 +/- ## ======================================= Coverage 96.52% 96.52% ======================================= Files 66 66 Lines 4983 4983 Branches 873 873 ======================================= Hits 4810 4810 Misses 97 97 Partials 76 76 ``` | [Flag](https://app.codecov.io/gh/oamg/convert2rhel/pull/1345/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/1345/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `91.94% <ø> (ø)` | | | [centos-linux-8](https://app.codecov.io/gh/oamg/convert2rhel/pull/1345/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `92.83% <ø> (ø)` | | | [centos-linux-9](https://app.codecov.io/gh/oamg/convert2rhel/pull/1345/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `92.87% <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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[has-bot]

This PR does not require integration tests to be run.

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