CI: Only MSRV-test published ash and ash-window crates

[MarijnS95]

bytemuck recently bumped its MSRV to 1.60 which is incompatible with what we're currently advertising. Fortunately this doesn't affect MSRV of the publicly published crates, but only dev-dependencies inside ash-window via winit: make sure the CI doesn't reject this.

$ cargo tree -i bytemuck
bytemuck v1.12.3
├── image v0.24.4
│   └── examples v0.1.0 (ash/examples)
├── safe_arch v0.5.2
│   └── tiny-skia v0.7.0
│       └── sctk-adwaita v0.4.3
│           └── winit v0.27.5
│               └── examples v0.1.0 (ash/examples)
│               [dev-dependencies]
│               └── ash-window v0.11.0 (ash/ash-window)
│                   └── examples v0.1.0 (ash/examples)
├── tiny-skia v0.7.0 (*)
└── tiny-skia-path v0.7.0
    └── tiny-skia v0.7.0 (*)