Bump com.diffplug.spotless:spotless-plugin-gradle

Bumps the gradle group in /codegen with 1 update: [com.diffplug.spotless:spotless-plugin-gradle](https://github.com/diffplug/spotless).


Updates `com.diffplug.spotless:spotless-plugin-gradle` from 8.0.0 to 8.1.0
- [Release notes](https://github.com/diffplug/spotless/releases)
- [Changelog](https://github.com/diffplug/spotless/blob/main/CHANGES.md)
- [Commits](diffplug/spotless@gradle/8.0.0...gradle/8.1.0)

---
updated-dependencies:
- dependency-name: com.diffplug.spotless:spotless-plugin-gradle
  dependency-version: 8.1.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: gradle
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

codegen/gradle/libs.versions.toml

@@ -3,7 +3,7 @@ junit5 = "6.0.1"
 smithy = "1.64.0"
 test-logger-plugin = "4.0.0"
 spotbugs = "6.0.22"
-spotless = "8.0.0"
+spotless = "8.1.0"
 smithy-gradle-plugins = "1.3.0"
 dep-analysis = "3.4.1"
 jsoup = "1.21.2"