Update dependency pdm-backend to v2.3.2 (#221)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [pdm-backend](https://togithub.com/pdm-project/pdm-backend) |
build-system.requires | patch | `==2.3.1` -> `==2.3.2` |

---

### Release Notes

<details>
<summary>pdm-project/pdm-backend (pdm-backend)</summary>

###
[`v2.3.2`](https://togithub.com/pdm-project/pdm-backend/releases/tag/2.3.2)

[Compare
Source](https://togithub.com/pdm-project/pdm-backend/compare/2.3.1...2.3.2)

#####    🐞 Bug Fixes

- Detect src layout only if it exists and included by build config  - 
by [@&#8203;frostming](https://togithub.com/frostming)
[<samp>(9466c)</samp>](https://togithub.com/pdm-project/pdm-backend/commit/9466c66)
- Use compatible is_relative_to for Python 3.8  -  by
[@&#8203;frostming](https://togithub.com/frostming)
[<samp>(30c46)</samp>](https://togithub.com/pdm-project/pdm-backend/commit/30c4614)

#####    📝 Documentation

- Update the logo url  -  by
[@&#8203;frostming](https://togithub.com/frostming)
[<samp>(fd5ef)</samp>](https://togithub.com/pdm-project/pdm-backend/commit/fd5eff3)

#####     [View changes on
GitHub](https://togithub.com/pdm-project/pdm-backend/compare/2.3.1...2.3.2)

</details>

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pyproject.toml

@@ -143,5 +143,5 @@ known-first-party = ["mex", "tests"]
 convention = "google"
 
 [build-system]
-requires = ["pdm-backend==2.3.1"]
+requires = ["pdm-backend==2.3.2"]
 build-backend = "pdm.backend"