[Tidy first] move non-circular import to top of manifest.py

[MichelleArk]

resolves #N/A

Problem

Nested import assuming a cycle

Solution

Move import to top of file since there is no cycle!

Checklist

• [x] I have read the contributing guide and understand what's expected of me
• [x] I have run this code in development and it appears to resolve the stated issue
• [x] This PR includes tests, or tests are not required/relevant for this PR
• [x] This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• [x] This PR includes type annotations for new and modified functions

[github-actions[bot]]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[codecov[bot]]

Codecov Report

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

Project coverage is 88.83%. Comparing base (71a8a41) to head (fa6e0ef).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #10333 +/- ## ======================================= Coverage 88.83% 88.83% ======================================= Files 180 180 Lines 22490 22490 ======================================= Hits 19980 19980 Misses 2510 2510 ``` | [Flag](https://app.codecov.io/gh/dbt-labs/dbt-core/pull/10333/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dbt-labs) | Coverage Δ | | |---|---|---| | [integration](https://app.codecov.io/gh/dbt-labs/dbt-core/pull/10333/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dbt-labs) | `86.21% <100.00%> (+0.02%)` | :arrow_up: | | [unit](https://app.codecov.io/gh/dbt-labs/dbt-core/pull/10333/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dbt-labs) | `62.19% <100.00%> (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=dbt-labs#carryforward-flags-in-the-pull-request-comment) to find out more.

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