ci: Upgrade ubuntu:25.04 for the PowerPC64LE test

Update the last remaining image.

extswsli in ld64.so

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 && \
@@ -13,6 +12,5 @@ ENV CARGO_TARGET_POWERPC64LE_UNKNOWN_LINUX_GNU_LINKER="$TOOLCHAIN_PREFIX"gcc \
     CARGO_TARGET_POWERPC64LE_UNKNOWN_LINUX_GNU_RUNNER=qemu-ppc64le-static \
     AR_powerpc64le_unknown_linux_gnu="$TOOLCHAIN_PREFIX"ar \
     CC_powerpc64le_unknown_linux_gnu="$TOOLCHAIN_PREFIX"gcc \
-    QEMU_CPU=POWER8 \
     QEMU_LD_PREFIX=/usr/powerpc64le-linux-gnu \
     RUST_TEST_THREADS=1