chore(deps): update gradle docker tag to v9 (#44)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: Thor Tudal Lauridsen <30320530+thorlauridsen@users.noreply.github.com>

Author: renovate[bot]

docker/Dockerfile

@@ -1,5 +1,5 @@
 # Stage 1: Build the application using a Gradle image with JDK 21.
-FROM gradle:8.14.3-jdk21-corretto AS builder
+FROM gradle:9.0.0-jdk21-corretto AS builder
 WORKDIR /home/gradle/project
 
 # Copy Gradle files from the correct locations.