Fix a formatting error in the "missing argument" error

[BlobCodes]

Closes #10324

Before:

After:

[kostya]

offtopic, what is this shell in screenshots?

[BlobCodes]

@kostya
Terminal-Emulator: Konsole (with Fluent Design Qt Theme for Kvantum)
Shell: zsh (with romkatv/powerlevel10k theme)

[docelic]

But this general style of prompts is otherwise known as "airline":

https://unix.stackexchange.com/questions/154012/terminal-colors-for-vim-airline-and-tmux-tmuxline

[Sija]

Suggested change

	io << message
	io << '\n'
	io.puts message

[Sija]

Suggested change

	str << single_message
	str << '\n'
	str.puts single_message

[BlobCodes]

@Sija I don't know if it's a good idea to use io.puts instead of io << '\n', because in src/compiler/crystal/semantic/call_error.cr, mostly the second style is used and I want to keep it consistent.

Examples:
l.593:

            str << "Did you mean '#{similar_name}'?"
            str << '\n'

l.323:

        str << ")\n"

The word "puts" however is not even included in this document.
Any thoughts on which style to use?

[asterite]

Both are equivalent so it's the same. I wouldn't worry about such things.

[Sija]

@BlobCodes puts is 'simpler' since it adds the trailing newline for you, but as @asterite mentioned both do the same thing.