Update Rust crate serde-untagged to v0.1.8 (#15504)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [serde-untagged](https://redirect.github.com/dtolnay/serde-untagged) |
workspace.dependencies | patch | `0.1.7` -> `0.1.8` |

---

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### Release Notes

<details>
<summary>dtolnay/serde-untagged (serde-untagged)</summary>

###
[`v0.1.8`](https://redirect.github.com/dtolnay/serde-untagged/releases/tag/0.1.8)

[Compare
Source](https://redirect.github.com/dtolnay/serde-untagged/compare/0.1.7...0.1.8)

- Add support for `visit_none`
([#&#8203;10](https://redirect.github.com/dtolnay/serde-untagged/issues/10),
thanks [@&#8203;epage](https://redirect.github.com/epage))

</details>

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Cargo.lock

@@ -3821,9 +3821,9 @@ dependencies = [
 
 [[package]]
 name = "serde-untagged"
-version = "0.1.7"
+version = "0.1.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "299d9c19d7d466db4ab10addd5703e4c615dec2a5a16dbbafe191045e87ee66e"
+checksum = "34836a629bcbc6f1afdf0907a744870039b1e14c0561cb26094fa683b158eff3"
 dependencies = [
  "erased-serde",
  "serde",