Fix incorrect test for options_.posterior_sampler_options.posterior_sampling_method

Thanks to checkcode().
11 jobs for master in 66 minutes and 40 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #16422
build_binaries

00:10:59

passed #16423
build_doc

00:01:38

 
  Test And Pkg
passed #16426
macOS
pkg_macOS

00:12:56

passed #16424
pkg_source

00:01:36

passed #16425
pkg_windows

00:32:11

passed #16430
test_dynare++

00:16:04

passed #16427
test_matlab

00:54:36

manual #16429
allowed to fail manual
test_octave
manual #16428
allowed to fail manual
test_old_matlab
 
  Deploy
passed #16431
restricted
deploy_manual_unstable

00:00:10

passed #16432
restricted
deploy_snapshot_unstable

00:00:51