Update Rust crate toml_edit to 0.21 (#515)

[![Mend
Renovate](https://app.renovatebot.com/images/banner.svg)](https://renovatebot.com)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [toml_edit](https://togithub.com/toml-rs/toml) | dependencies | minor
| `0.20` -> `0.21` |

---

### Release Notes

<details>
<summary>toml-rs/toml (toml_edit)</summary>

###
[`v0.21.0`](https://togithub.com/toml-rs/toml/compare/v0.20.7...v0.21.0)

[Compare
Source](https://togithub.com/toml-rs/toml/compare/v0.20.7...v0.21.0)

###
[`v0.20.7`](https://togithub.com/toml-rs/toml/compare/v0.20.6...v0.20.7)

[Compare
Source](https://togithub.com/toml-rs/toml/compare/v0.20.6...v0.20.7)

###
[`v0.20.6`](https://togithub.com/toml-rs/toml/compare/v0.20.5...v0.20.6)

[Compare
Source](https://togithub.com/toml-rs/toml/compare/v0.20.5...v0.20.6)

###
[`v0.20.5`](https://togithub.com/toml-rs/toml/compare/v0.20.4...v0.20.5)

[Compare
Source](https://togithub.com/toml-rs/toml/compare/v0.20.4...v0.20.5)

###
[`v0.20.4`](https://togithub.com/toml-rs/toml/compare/v0.20.3...v0.20.4)

[Compare
Source](https://togithub.com/toml-rs/toml/compare/v0.20.3...v0.20.4)

###
[`v0.20.3`](https://togithub.com/toml-rs/toml/compare/v0.20.2...v0.20.3)

[Compare
Source](https://togithub.com/toml-rs/toml/compare/v0.20.2...v0.20.3)

###
[`v0.20.2`](https://togithub.com/toml-rs/toml/compare/v0.20.1...v0.20.2)

[Compare
Source](https://togithub.com/toml-rs/toml/compare/v0.20.1...v0.20.2)

###
[`v0.20.1`](https://togithub.com/toml-rs/toml/compare/v0.20.0...v0.20.1)

[Compare
Source](https://togithub.com/toml-rs/toml/compare/v0.20.0...v0.20.1)

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined),
Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you
are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the
rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update
again.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
this box

---

This PR has been generated by [Mend
Renovate](https://www.mend.io/free-developer-tools/renovate/). View
repository job log [here](https://developer.mend.io/github/agbrs/agb).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzNy40Ni4wIiwidXBkYXRlZEluVmVyIjoiMzcuNDYuMCIsInRhcmdldEJyYW5jaCI6Im1hc3RlciJ9-->