fix(test): the vkgen drift check runs wherever the Vulkan SDK is

`ls a b` fails when `a` is missing even though `b` exists, so with VULKAN_SDK unset the
guard skipped the check on a Mac that has the SDK under ~/VulkanSDK.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tools/ludic-cli/test.ludic

@@ -811,7 +811,7 @@ function cmd_dev_test() -> int {
 
   # and the Vulkan one: vk_api.ludic + vk_thunks.ll regenerated from the registry's vk.xml,
   # which comes with the Vulkan SDK - so this guard runs wherever the SDK is installed
-  if shq("ls $VULKAN_SDK/share/vulkan/registry/vk.xml $HOME/VulkanSDK/*/macOS/share/vulkan/registry/vk.xml >/dev/null 2>&1") {
+  if shq("ls $VULKAN_SDK/share/vulkan/registry/vk.xml $HOME/VulkanSDK/*/macOS/share/vulkan/registry/vk.xml 2>/dev/null | grep -q vk.xml") {
     if shq(`bin/ludic-dev vkgen --check > {tmp_dir()}/vkgen.out 2>&1`) {
       ok("ludic-dev vkgen regenerates vk_api.ludic + vk_thunks.ll byte-identically")
     } else { bad2("ludic-dev vkgen --check", capture_line(`tail -1 {tmp_dir()}/vkgen.out`)) }