build: Bump Spotless to 8.8.0 (#5720)

* fix(spring): Support Spring Boot 4.1

Bump OpenTelemetry and Spring Boot dependencies to compatible versions so the Spring Boot 4 OpenTelemetry sample works with Spring Boot 4.1.

Keep the Spring 7 sample on the repository Kotlin compiler version when importing the Spring Boot BOM, and add Spring Boot 4.1 to the system test matrix.

Fixes GH-5561

Co-Authored-By: Claude <noreply@anthropic.com>

* changelog

* build: Bump Kotlin to 2.3.21

Align the global Kotlin version with Spring Boot 4.1 and remove the now-unneeded Spring 7 BOM override.

Also remove unused Spring 7-specific Kotlin aliases from the version catalog.

Co-Authored-By: Claude <noreply@anthropic.com>

* build: Bump Spotless to 8.7.0

Update the Spotless Gradle plugin and apply the resulting formatting changes.

Co-Authored-By: Claude <noreply@anthropic.com>

* build: Bump Spotless to 8.8.0

Update the Spotless Gradle plugin to the latest available release.

Co-Authored-By: Claude <noreply@anthropic.com>

* Format code

* Apply suggestion from @adinauer

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Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Sentry Github Bot <bot+github-bot@sentry.io>