build: Bump micronaut-gradle-plugins from 4.1.5 to 4.2.1 (#174)

Bumps [micronaut-gradle-plugins](https://github.com/micronaut-projects/micronaut-build) from 4.1.5 to 4.2.1.
- [Release notes](https://github.com/micronaut-projects/micronaut-build/releases)
- [Commits](micronaut-projects/micronaut-build@v4.1.5...v4.2.1)

---
updated-dependencies:
- dependency-name: io.micronaut.build.internal:micronaut-gradle-plugins
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

build.gradle

@@ -4,7 +4,7 @@ buildscript {
         gradlePluginPortal()
     }
     dependencies {
-        classpath "io.micronaut.build.internal:micronaut-gradle-plugins:4.1.5"
+        classpath "io.micronaut.build.internal:micronaut-gradle-plugins:4.2.1"
     }
 }