chore(deps): update dependency flask to v3.1.2 (#150)

This PR contains the following updates:

| Package | Change | Age | Confidence |
|---|---|---|---|
| [Flask](https://github.com/pallets/flask) ([changelog](https://flask.palletsprojects.com/page/changes/)) | `==3.1.1` -> `==3.1.2` | [![age](https://developer.mend.io/api/mc/badges/age/pypi/flask/3.1.2?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/flask/3.1.1/3.1.2?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>pallets/flask (Flask)</summary>

### [`v3.1.2`](https://github.com/pallets/flask/blob/HEAD/CHANGES.rst#Version-312)

[Compare Source](https://github.com/pallets/flask/compare/3.1.1...3.1.2)

Released 2025-08-19

- `stream_with_context` does not fail inside async views. :issue:`5774`
- When using `follow_redirects` in the test client, the final state
  of `session` is correct. :issue:`5786`
- Relax type hint for passing bytes IO to `send_file`. :issue:`5776`

</details>

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Reviewed-on: #150
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.ARCHIVE/requirements.txt

@@ -1,7 +1,7 @@
 certifi==2025.8.3
 charset-normalizer==3.4.3
 click==8.2.2
-Flask==3.1.1
+Flask==3.1.2
 Flask-WTF==1.2.2
 idna==3.10
 itsdangerous==2.2.0