test: fix luaunit/assertions_error_test for Tarantool 3.2 and newer

With Tarantool 3.2 and newer the test fails with:

```
...luatest/test/luaunit/assertions_error_test.lua:244: Unexpected error trace,
expected: {file = "/home/runner/work/luatest/luatest/luatest/assertions.lua", line = 102},
actual: {
    file = "...k/luatest/luatest/test/luaunit/assertions_error_test.lua",
    line = 236,
}
```

On older Tarantool versions the error trace isn't checked because
`tarantool._internal.trace_check_is_required` isn't defined there.
Tarantool 3.2 is the first version that defines this internal function.
Since `error.raise` used by the test resides in 'builtin/error.lua',
stack trace checking is enabled for this function.

The problem is `error.raise()` does not change the original error trace
while `t.assert_error_covers()` expects the trace to point to the place
where `error.raise()` was invoked. Let's use `box.error()` instead so
the new error has the expected trace.

Also change `box.error.ILLEGAL_PARAMS` to `box.error.UNSUPPORTED` for
the check to pass because in Tarantool 3.2 the former was changed to
`{type = 'IllegalParams'}`.

Author: nshy

test/luaunit/assertions_error_test.lua

@@ -235,13 +235,13 @@ function g.test_assert_errorCovers()
     t.assert_error_covers({type = 'ClientError', code = 0}, box.error, 0)
     local err = box.error.new(box.error.UNKNOWN)
     if err.set_prev ~= nil then
-        err:set_prev(box.error.new(box.error.ILLEGAL_PARAMS, 'foo'))
+        err:set_prev(box.error.new(box.error.UNSUPPORTED, 'foo', 'bar'))
         expected = {
             type = 'ClientError',
             code = box.error.UNKNOWN,
-            prev = {code = box.error.ILLEGAL_PARAMS}
+            prev = {type = 'ClientError', code = box.error.UNSUPPORTED}
         }
-        t.assert_error_covers(expected, err.raise, err)
+        t.assert_error_covers(expected, box.error, err)
     end
 
     -- test assert failure due to unexpected error trace