Update dependency pdm-backend to v2.4.2 (#308)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [pdm-backend](https://github.com/pdm-project/pdm-backend) |
build-system.requires | patch | `==2.4.1` -> `==2.4.2` |

---

### Release Notes

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

###
[`v2.4.2`](https://github.com/pdm-project/pdm-backend/releases/tag/2.4.2)

[Compare
Source](https://github.com/pdm-project/pdm-backend/compare/2.4.1...2.4.2)

#####    🚀 Features

- Use fallback_version for source = "call"  -  by
[@&#8203;frostming](https://github.com/frostming) in
[https://github.com/pdm-project/pdm-backend/issues/264](https://github.com/pdm-project/pdm-backend/issues/264)
[<samp>(16562)</samp>](https://github.com/pdm-project/pdm-backend/commit/1656230)

#####    🐞 Bug Fixes

- Update to pyproject_metadata 0.9.0b5  -  by
[@&#8203;henryiii](https://github.com/henryiii) in
[https://github.com/pdm-project/pdm-backend/issues/263](https://github.com/pdm-project/pdm-backend/issues/263)
[<samp>(67fb7)</samp>](https://github.com/pdm-project/pdm-backend/commit/67fb709)

#####     [View changes on
GitHub](https://github.com/pdm-project/pdm-backend/compare/2.4.1...2.4.2)

</details>

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pyproject.toml

@@ -155,5 +155,5 @@ known-first-party = ["mex", "tests"]
 convention = "google"
 
 [build-system]
-requires = ["pdm-backend==2.4.1"]
+requires = ["pdm-backend==2.4.2"]
 build-backend = "pdm.backend"