Update Rust crate proc-macro2 to v1.0.86 (#15940)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [proc-macro2](https://togithub.com/dtolnay/proc-macro2) | dependencies
| patch | `1.0.81` -> `1.0.86` |

---

### Release Notes

<details>
<summary>dtolnay/proc-macro2 (proc-macro2)</summary>

###
[`v1.0.86`](https://togithub.com/dtolnay/proc-macro2/releases/tag/1.0.86)

[Compare
Source](https://togithub.com/dtolnay/proc-macro2/compare/1.0.85...1.0.86)

-   Documentation improvements

###
[`v1.0.85`](https://togithub.com/dtolnay/proc-macro2/releases/tag/1.0.85)

[Compare
Source](https://togithub.com/dtolnay/proc-macro2/compare/1.0.84...1.0.85)

- Mark some tests as only for 64-bit targets
([#&#8203;463](https://togithub.com/dtolnay/proc-macro2/issues/463))

###
[`v1.0.84`](https://togithub.com/dtolnay/proc-macro2/releases/tag/1.0.84)

[Compare
Source](https://togithub.com/dtolnay/proc-macro2/compare/1.0.83...1.0.84)

- Documentation improvements
([#&#8203;455](https://togithub.com/dtolnay/proc-macro2/issues/455),
thanks
[@&#8203;CensoredUsername](https://togithub.com/CensoredUsername))

###
[`v1.0.83`](https://togithub.com/dtolnay/proc-macro2/releases/tag/1.0.83)

[Compare
Source](https://togithub.com/dtolnay/proc-macro2/compare/1.0.82...1.0.83)

- Optimize the representation of `Ident`
([#&#8203;462](https://togithub.com/dtolnay/proc-macro2/issues/462))

###
[`v1.0.82`](https://togithub.com/dtolnay/proc-macro2/releases/tag/1.0.82)

[Compare
Source](https://togithub.com/dtolnay/proc-macro2/compare/1.0.81...1.0.82)

- Resolve unexpected_cfgs warning
([#&#8203;456](https://togithub.com/dtolnay/proc-macro2/issues/456))

</details>

---

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Release Notes:

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