chore: update dependency com.puppycrawl.tools:checkstyle to v10.21.0 (#67)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.puppycrawl.tools:checkstyle](https://checkstyle.org/)
([source](https://redirect.github.com/checkstyle/checkstyle)) |
`10.18.2` -> `10.21.0` |
[![age](https://developer.mend.io/api/mc/badges/age/maven/com.puppycrawl.tools:checkstyle/10.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/maven/com.puppycrawl.tools:checkstyle/10.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/maven/com.puppycrawl.tools:checkstyle/10.18.2/10.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/maven/com.puppycrawl.tools:checkstyle/10.18.2/10.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>checkstyle/checkstyle
(com.puppycrawl.tools:checkstyle)</summary>

###
[`v10.21.0`](https://redirect.github.com/checkstyle/checkstyle/compare/checkstyle-10.20.2...checkstyle-10.21.0)

[Compare
Source](https://redirect.github.com/checkstyle/checkstyle/compare/checkstyle-10.20.2...checkstyle-10.21.0)

###
[`v10.20.2`](https://redirect.github.com/checkstyle/checkstyle/compare/checkstyle-10.20.1...checkstyle-10.20.2)

[Compare
Source](https://redirect.github.com/checkstyle/checkstyle/compare/checkstyle-10.20.1...checkstyle-10.20.2)

###
[`v10.20.1`](https://redirect.github.com/checkstyle/checkstyle/compare/checkstyle-10.20.0...checkstyle-10.20.1)

[Compare
Source](https://redirect.github.com/checkstyle/checkstyle/compare/checkstyle-10.20.0...checkstyle-10.20.1)

###
[`v10.20.0`](https://redirect.github.com/checkstyle/checkstyle/compare/checkstyle-10.19.0...checkstyle-10.20.0)

###
[`v10.19.0`](https://redirect.github.com/checkstyle/checkstyle/compare/checkstyle-10.18.2...checkstyle-10.19.0)

[Compare
Source](https://redirect.github.com/checkstyle/checkstyle/compare/checkstyle-10.18.2...checkstyle-10.19.0)

</details>

---

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---

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---

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gradle/libs.versions.toml

@@ -5,7 +5,7 @@ shadow = "8.3.3"
 juppiter = "0.4.0"
 spotless = "6.25.0"
 nexusPublish = "2.0.0"
-checkstyleTools = "10.18.2"
+checkstyleTools = "10.21.0"
 
 # testing
 junit = "5.11.2"