fix: use uppercase const name

[chadoh]

What

This fixes an issue where Rust Analyzer sometimes complains that:

constant `symbol` should have UPPER_SNAKE_CASE name

Why

When using symbol_short!, as recommended by the Getting Started → Hello World tutorial, I was getting confusing warnings from Rust Analyzer:

Known limitations

Why not use this instead?

Ok(_) => quote! {
    #crate_path::Symbol::short(#s)
}