Bump io.freefair.lombok from 8.6 to 8.12.2.1 in /backend (#48)

Bumps [io.freefair.lombok](https://github.com/freefair/gradle-plugins) from 8.6 to 8.12.2.1.
- [Release notes](https://github.com/freefair/gradle-plugins/releases)
- [Commits](freefair/gradle-plugins@8.6...8.12.2.1)

---
updated-dependencies:
- dependency-name: io.freefair.lombok
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Malte Schwitters <[email protected]>

Author: dependabot[bot]

backend/build.gradle

@@ -2,7 +2,7 @@ plugins {
     id 'java'
     id 'org.springframework.boot' version '3.4.3'
     id 'io.spring.dependency-management' version '1.1.7'
-    id 'io.freefair.lombok' version '8.6'
+    id 'io.freefair.lombok' version '8.12.2.1'
 }
 
 group = 'org.eventplanner'