vulkan: Update docker image to Ubuntu 26.04 to enable glslc features (ggml-org#17439)

26.04 provides these

Signed-off-by: Eric Curtin <[email protected]>

Author: ericcurtin

.devops/vulkan.Dockerfile

@@ -1,9 +1,7 @@
-ARG UBUNTU_VERSION=25.10
+ARG UBUNTU_VERSION=26.04
 
 FROM ubuntu:$UBUNTU_VERSION AS build
 
-# Ref: https://vulkan.lunarg.com/doc/sdk/latest/linux/getting_started.html
-
 # Install build tools
 RUN apt update && apt install -y git build-essential cmake wget xz-utils