Fix(error): Printing a new line to avoid overwriting error code after \r

[Suryansh-Dey]

What does this PR try to resolve?

Closes #17343
Changes:
Added newline using writeln!(gctx.shell().err());
Reason:
Could have used format!("\n{err}") but if there's an in-progress status line, gctx.shell().err() would erase it then print a newline. If you want I can switch to format option but this feels practically safer.

How to test and review this PR?

• Run cargo test -p cargo --test testsuite -- run::exit_code run::exit_code_verbose And both the tests passes.
• Make a program in windows

fn main() {
    print!("hewwo\r");
    std::process::exit(1);
}

then run cargo run. It prints error message just below.

(Compiling for windows almost killed my laptop)

Before (current cargo on windows)

[rustbot]

r? @epage

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Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @epage, @weihanglo
• @epage, @weihanglo expanded to epage, weihanglo
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[epage]

For myself, I prefer describing why inline instead of pointing to a comment, like

Ensure a newline between user and cargo's output, especially with trailing "\r"

View changes since the review

[Suryansh-Dey]

Should I keep the URL in more like this?:
Ensure a newline between user and cargo's output, especially with trailing "\r". More

Once I get your opinion I am ready to proceed