Auto merge of #113271 - matthiaskrgr:rollup-2ik4vaj, r=matthiaskrgr

Rollup of 3 pull requests

Successful merges:

 - #113253 (Fixed documentation of from<CString> for Rc<CStr>: Arc -> Rc)
 - #113258 (Migrate GUI colors test to original CSS color format)
 - #113259 (Suggest `x build library` for a custom toolchain that fails to load `core`)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

alloc/src/ffi/c_str.rs

@@ -888,7 +888,7 @@ impl From<&CStr> for Arc<CStr> {
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<CString> for Rc<CStr> {
     /// Converts a [`CString`] into an <code>[Rc]<[CStr]></code> by moving the [`CString`]
-    /// data into a new [`Arc`] buffer.
+    /// data into a new [`Rc`] buffer.
     #[inline]
     fn from(s: CString) -> Rc<CStr> {
         let rc: Rc<[u8]> = Rc::from(s.into_inner());