Fix function calls inference in pipes

[sobolevn]

So, why did I make this change?

In some cases return_.fn_arity() was returning None, because return_ was not a function type, but Type::Var { type_ }. Which does not have an arity.

Why is it safe not to check the arity here? Because it will be checked in the second self.expr_typer.do_infer_call_with_known_fun call here:

gleam/compiler-core/src/type_/pipe.rs

Lines 249 to 260 in 72f4ac9

	let (function, args, type_) = self.expr_typer.do_infer_call_with_known_fun(
	function,
	args,
	location,
	CallKind::Function,
	);
	TypedExpr::Call {
	location,
	type_,
	args,
	fun: Box::new(function),
	}

Closes #3515

[sobolevn]

CC @nohzafk @giacomocavalieri

[sobolevn]

Oups, somehow unrelated changes got into this PR, removing and updating.

[lpil]

Thank you