Tracking issue for release notes of #159730: allow accessing the contents of UnsafeCell without going through get

This issue tracks the release notes text for #159730.

cc @RalfJung, @jhpratt -- original issue/PR authors and assignees for drafting text

See the forge.rust-lang.org chapter about release notes for an overview of how the release team makes use of these tracking issues.

Release notes text

This section should be edited to specify the correct category(s) for the change, with succinct description(s) of what changed. Some things worth considering:

• Does this need an additional compat notes section?
• Was this a libs stabilization that should have additional headers to list new APIs under Stabilized APIs and Const Stabilized APIs?

# Language
- We now [guarantee](https://github.com/rust-lang/rust/pull/159730) that the contents of an `UnsafeCell` can be accessed without going through `get`
   - [The `invalid_reference_casting` lint was adjusted accordingly](https://github.com/rust-lang/rust/pull/159960)

[!TIP]
Use the previous releases for inspiration on how to write the release notes text and which categories to pick.

Release blog section

If this change is notable enough for inclusion in the blog post then this section should be edited to contain a draft for the blog post. Otherwise leave it empty.

[!NOTE]

If a blog post section is required the release-blog-post label should be added (@rustbot label +release-blog-post) to this issue as otherwise it may be missed by the release team.

Review the Forge release-notes guidance and previous releases for category conventions. Update the Release notes text section with the appropriate category and concise description for #159730, including the lint adjustment; leave the blog section empty unless the change is notable enough for a blog post.