build(deps): update dependency org.apache.maven.plugins:maven-checkst…

…yle-plugin to v3.6.0 (#3428)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [org.apache.maven.plugins:maven-checkstyle-plugin](https://maven.apache.org/plugins/) | `3.5.0` -> `3.6.0` | [![age](https://developer.mend.io/api/mc/badges/age/maven/org.apache.maven.plugins:maven-checkstyle-plugin/3.6.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/maven/org.apache.maven.plugins:maven-checkstyle-plugin/3.6.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/maven/org.apache.maven.plugins:maven-checkstyle-plugin/3.5.0/3.6.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/maven/org.apache.maven.plugins:maven-checkstyle-plugin/3.5.0/3.6.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

---

### 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 was generated by [Mend Renovate](https://mend.io/renovate/). View the [repository job log](https://developer.mend.io/github/googleapis/java-spanner).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzOC4xMjAuMSIsInVwZGF0ZWRJblZlciI6IjM4LjEyMC4xIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6W119-->

samples/snippets/pom.xml

@@ -192,7 +192,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-checkstyle-plugin</artifactId>
-        <version>3.5.0</version>
+        <version>3.6.0</version>
         <configuration>
           <!-- exclude protoc generated file from checkstyle validation -->
           <excludes>**/SingerProto.java</excludes>