ci: don't install no_std targets

[mkroening]

Summary of the PR

With https://github.com/rust-vmm/rust-vmm-container/pull/94, this is included in the image. We can merge this, once rust-vmm-ci is updated.

See https://github.com/rust-vmm/vm-fdt/pull/68#discussion_r1392311370.

Requirements

Before submitting your PR, please make sure you addressed the following requirements:

• [x] All commits in this PR are signed (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [ ] All added/changed functionality has a corresponding unit/integration test.
• [ ] All added/changed public-facing functionality has entries in the "Upcoming Release" section of CHANGELOG.md (if no such section exists, please create one).
• [x] Any newly added unsafe code is properly documented.

[mkroening]

@danielverkamp, I have rebased on the latest main, updated rust-vmm-ci to the latest main and adjusted the coverage score to pass CI. :)