tests: add tests for checking fixed array .sort() errors

[yuyi98]

This PR add tests for checking fixed array .sort() errors.

fn main() {
	mut arr := [3, 2, 1]!
	arr.sort(a < b, a)
	arr.sort(a == b)
	arr.sort(a > a)
	arr.sort(c > d)
}

PS D:\Test\v\tt1> v run .
tt1.v:3:6: error: expected 0 or 1 argument, but got 2
    1 | fn main() {
    2 |     mut arr := [3, 2, 1]!
    3 |     arr.sort(a < b, a)
      |         ~~~~~~~~~~~~~~
    4 |     arr.sort(a == b)
    5 |     arr.sort(a > a)
tt1.v:4:6: error: `.sort()` can only use `<` or `>` comparison
    2 |     mut arr := [3, 2, 1]!
    3 |     arr.sort(a < b, a)
    4 |     arr.sort(a == b)
      |         ~~~~~~~~~~~~
    5 |     arr.sort(a > a)
    6 |     arr.sort(c > d)
tt1.v:5:6: error: `.sort()` cannot use same argument
    3 |     arr.sort(a < b, a)
    4 |     arr.sort(a == b)
    5 |     arr.sort(a > a)
      |         ~~~~~~~~~~~
    6 |     arr.sort(c > d)
    7 | }
tt1.v:6:11: error: can not access external variable `c`
    4 |     arr.sort(a == b)
    5 |     arr.sort(a > a)
    6 |     arr.sort(c > d)
      |              ^
    7 | }
tt1.v:6:6: error: `.sort()` can only use `a` or `b` as argument, e.g. `arr.sort(a < b)`
    4 |     arr.sort(a == b)
    5 |     arr.sort(a > a)
    6 |     arr.sort(c > d)
      |         ~~~~~~~~~~~
    7 | }
tt1.v:6:11: error: undefined ident: `c`
    4 |     arr.sort(a == b)
    5 |     arr.sort(a > a)
    6 |     arr.sort(c > d)
      |              ^
    7 | }
tt1.v:6:15: error: undefined ident: `d`
    4 |     arr.sort(a == b)
    5 |     arr.sort(a > a)
    6 |     arr.sort(c > d)
      |                  ^
    7 | }

fn ret_array() [3]int {
	return [1, 3, 2]!
}

fn main() {
	ret_array().sort()
}

PS D:\Test\v\tt1> v run .
tt1.v:6:14: error: the `sort()` method can be called only on mutable receivers, but `ret_array()` is a call expression
    4 |
    5 | fn main() {
    6 |     ret_array().sort()
      |                 ~~~~~~
    7 | }
tt1.v:6:2: error: cannot pass expression as `mut`
    4 |
    5 | fn main() {
    6 |     ret_array().sort()
      |     ~~~~~~~~~~~
    7 | }

_{Huly®: V_0.6-21105}

[spytheman]

Excellent work.
Thank you 🙇🏻‍♂️ .