Overrides with dated nightly in file override and simple stable commandline override lead to unholy hybrid toolchain that doesn't exist

Checklist

I've looked through the issues and pull requests for similar reports

Describe your issue

I've got a project with

# rust-toolchain.toml
[toolchain]
channel = "nightly-2024-08-02"
components = ["rust-src", "rustfmt", "clippy"]

and I invoke cross with cross +stable build. That same thing works with cargo. With cross I end up with:

+ rustup toolchain add stable-2024-08-02-x86_64-unknown-linux-gnu --profile minimal --force-non-host
info: syncing channel updates for 'stable-2024-08-02-x86_64-unknown-linux-gnu'
error: no release found for 'stable-2024-08-02'
Error: 
   0: couldn't install toolchain `stable-2024-08-02-x86_64-unknown-linux-gnu`
   1: `rustup toolchain add stable-2024-08-02-x86_64-unknown-linux-gnu --profile minimal --force-non-host` failed with exit status: 1

cross version

cross v0.2.5 (https://github.com/cross-rs/cross?rev=1b8cf50d20180c1a394099e608141480f934b7f7#1b8cf50d)

Example

No response

Additional information / notes

No response

We need to remove date here

cross/src/rustc.rs

Lines 215 to 230 in 1901fd7

    
           /// Merge a "picked" toolchain, overriding set fields. 
        
           pub fn with_picked(self, picked: Toolchain) -> Result<Self> { 
        
               let date = picked.date.or(self.date); 
        
               let host = picked 
        
                   .host 
        
                   .map_or(Ok(self.host), ImagePlatform::from_target)?; 
        
               let channel = picked.channel; 
        
               Ok(QualifiedToolchain::new( 
        
                   &channel, 
        
                   &date, 
        
                   &host, 
        
                   &self.sysroot, 
        
                   false, 
        
               )) 
        
           }

if channel is not nightly

	/// Merge a "picked" toolchain, overriding set fields.
	pub fn with_picked(self, picked: Toolchain) -> Result<Self> {
	let date = picked.date.or(self.date);
	let host = picked
	.host
	.map_or(Ok(self.host), ImagePlatform::from_target)?;
	let channel = picked.channel;

	Ok(QualifiedToolchain::new(
	&channel,
	&date,
	&host,
	&self.sysroot,
	false,
	))
	}