Bump DCGM to 4.6.0-1 to fix broken repo dependency

NVIDIA removed datacenter-gpu-manager-4-core 1:4.5.3-1 from the
repository and published 1:4.6.0-1. The cuda13 and proprietary
packages still declared an exact-version dependency on 4.5.3-1 core,
making the old pin unresolvable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/VERSIONS

@@ -9,7 +9,7 @@ NCCL_TESTS_VERSION=2.13.10
 NVCC_VERSION=12.8
 CUBLAS_VERSION=13.1.1.3-1
 CUDA_USERSPACE_VERSION=13.0.96-1
-DCGM_VERSION=4.5.3-1
+DCGM_VERSION=4.6.0-1
 JOHN_JUMBO_COMMIT=67fcf9fe5a
 ROCM_VERSION=6.3.4
 ROCM_SMI_VERSION=7.4.0.60304-76~22.04