`vec_as_subscript2()` doesn't throw lossy cast errors correctly

[DavisVaughan]

library(vctrs)

vec_as_subscript(1.5)
#> Error:
#> ! Must subset elements with a valid subscript vector.
#> ✖ Can't convert from <double> to <integer> due to loss of precision.

vec_as_subscript2(1.5)
#> Error:
#> ! Must extract element with a single valid subscript.
#> ✖ Subscript has the wrong type `double`.
#> ℹ It must be logical, numeric, or character.

It looks like it was supposed to use a lossy cast body here:

vctrs/R/subscript.R

Lines 104 to 106 in 544cc70

	parent <- result$err$parent
	if (inherits(parent, "vctrs_error_cast_lossy")) {
	bullets <- new_cnd_bullets_subscript_lossy_cast(parent)

But it looks like parent is actually always NULL? It somehow isn't being set in the err object. Commenting out line 106 doesn't break any tests, so I'm assuming this just isn't tested