Test error class rather than snapshot for errors from other packages

[hfrick]

This looks like we are testing errors from tidyselect in various places. Example:

rsample/tests/testthat/_snaps/boot.md

Lines 17 to 22 in bdf12e1

	Code
	bootstraps(warpbreaks, strata = warpbreaks$tension)
	Condition
	Error in `bootstraps()`:
	! Can't select columns that don't exist.
	x Columns `L`, `L`, `L`, `L`, `L`, etc. don't exist.

If so, we should test the error class rather than the message, like here:

rsample/tests/testthat/test-compat-vctrs.R

Line 67 in bdf12e1

expect_error(vec_cast(x, x), class = "vctrs_error_incompatible_type")

[hfrick]

link to tidyselect: #413