…ure Linux 4

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# PR Summary
<!-- Summarize your PR between here and the checklist. -->
- Remove the x64 and ARM64 Azure Linux 4 mappings for the `preview` PMC channel.
- Preserve both Azure Linux 4 mappings for the `stable` PMC channel.
- Update the packaging tests to assert that preview releases do not map to Azure Linux 4 repositories.
## PR Context
<!-- Provide a little reasoning as to why this Pull Request helps and why you have opened it. -->
PowerShell preview and RC release tags select mappings with `channel: preview`. Azure Linux 4 should not receive preview PowerShell packages, so this removes only those two routing entries from `release/v7.7.0-rc.1`; stable publication remains unchanged.
Validation:
- `Invoke-Pester` for `test/packaging/packaging.tests.ps1`: passed 22 tests, failed 0.
- PowerShell parser check for the changed test file: passed with 0 errors.
- `git diff --check`: passed.
## PR Checklist
- [x] [PR has a meaningful title](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#pull-request---submission)
  - Use the present tense and imperative mood when describing your changes
- [x] [Summarized changes](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#pull-request---submission)
- [x] [Make sure all `.h`, `.cpp`, `.cs`, `.ps1` and `.psm1` files have the correct copyright header](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#pull-request---submission)
- [x] This PR is ready to merge. If this PR is a work in progress, please open this as a [Draft Pull Request and mark it as Ready to Review when it is ready to merge](https://docs.github.com/pull-requests/collaborating-with-pull-requests/proposing-changes-to-a-pull-request/about-pull-requests#draft-pull-requests).
- **[Breaking changes](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#making-breaking-changes)**
  - [x] None
  - **OR**
  - [ ] [Experimental feature(s) needed](https://github.com/MicrosoftDocs/PowerShell-Docs/blob/main/reference/7.5/Microsoft.PowerShell.Core/About/about_Experimental_Features.md)
    - [ ] Experimental feature name(s):
- **User-facing changes**
  - [x] Not Applicable
  - **OR**
  - [ ] [Documentation needed](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#pull-request---submission)
    - [ ] Issue filed:
- **Testing - New and feature**
  - [ ] N/A or can only be tested interactively
  - **OR**
  - [x] [Make sure you've added a new test if existing tests do not effectively test the code changed](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#before-submitting)

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#### AI description  (iteration 1)
#### PR Classification
Removal of unused/deprecated package mappings, a cleanup/configuration change to stop publishing preview packages to Azure Linux 4.

#### PR Summary
This PR removes the preview...