JetBrains CLion giving false positives in no_std nightly Rust, saying builtin types aren't `Sized`

Question

I am part of a project writing a kernel and OS in Rust. I am getting many false positives from the external linter (Clippy), such as:

The size for values of type &str cannot be known at compilation time
The size for values of type core::str::Utf8Error cannot be known at compilation time

etc.

I tried running Clippy in Terminal, and I just got other random warnings in my code (correctly).

Expected behavior: No incorrect errors
Received behavior: Incorrect errors