vulkan-headers, vulkan-tools: fix version

This fixes an assertion error in vulkan-loader on version == vulkan-headers.version:

assertion failed at /nix/store/ca66sbxzxlxlfpb579nxxnw97z2ql1gv-source/pkgs/development/libraries/vulkan-loader/default.nix:8:1

The sha256 for vulkan-headers and vulkan-tools are unchanged because
they were already set to the newer version. The correct version was
lost in the staging-next merge.