PIN docker image version.

Author: phipag

powertools-e2e-tests/src/test/resources/docker/Dockerfile

@@ -1,5 +1,5 @@
 # Use the official AWS SAM base image for Java 21
-FROM public.ecr.aws/sam/build-java21:latest
+FROM public.ecr.aws/sam/build-java21@sha256:a5554d68374e19450c6c88448516ac95a9acedc779f318040f5c230134b4e461
 
 # Install GraalVM dependencies
 RUN curl -4 -L https://download.oracle.com/graalvm/21/latest/graalvm-jdk-21_linux-x64_bin.tar.gz | tar -xvz