chore(deps)(deps): bump eclipse-temurin in /Backend

Bumps eclipse-temurin from 21-jre to 25-jre.

---
updated-dependencies:
- dependency-name: eclipse-temurin
  dependency-version: 25-jre
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Backend/Dockerfile

@@ -17,7 +17,7 @@ RUN ./gradlew clean build -x test
 RUN find . -name "*-plain.jar" -type f -delete
 
 # ===== Stage 2: Runtime – Minimaler JRE Container =====
-FROM eclipse-temurin:21-jre
+FROM eclipse-temurin:25-jre
 WORKDIR /app
 
 # Kopiere das erstellte Jar in den Runtime-Container