ci: Upgrade ubuntu:25.04 for the PowerPC64LE test

Update the last remaining image.

Author: tgross35

ci/docker/powerpc64le-unknown-linux-gnu/Dockerfile

@@ -1,5 +1,4 @@
-# FIXME(ppc): We want 25.04 but get SIGILLs
-ARG IMAGE=ubuntu:24.04
+ARG IMAGE=ubuntu:25.04
 FROM $IMAGE
 
 RUN apt-get update && \