TST: skip `Test_SVDS.test_small_sigma2` for float32 with PROPACK
TST: skip `Test_SVDS.test_small_sigma2` for float32 with PROPACK

This has been failing in CI for a while. There are lots of PROPACK
issues, so we'll just add one more skip for now. This test is
pretty sensitive, regular float32 tests all pass.

See gh-17004 for more details.

Also note that the skip condition had a problem, so ARPACK tests
would be skipped if PROPACK was not available - this is fixed now.

endolith/scipy,scipy/scipy,ilayn/scipy,anntzer/scipy,endolith/scipy,Stefan-Endres/scipy,andyfaff/scipy,WarrenWeckesser/scipy,anntzer/scipy,WarrenWeckesser/scipy,WarrenWeckesser/scipy,ilayn/scipy,anntzer/scipy,scipy/scipy,WarrenWeckesser/scipy,Stefan-Endres/scipy,andyfaff/scipy,ilayn/scipy,andyfaff/scipy,ilayn/scipy,andyfaff/scipy,WarrenWeckesser/scipy,mdhaber/scipy,endolith/scipy,Stefan-Endres/scipy,scipy/scipy,andyfaff/scipy,scipy/scipy,andyfaff/scipy,Stefan-Endres/scipy,Stefan-Endres/scipy,scipy/scipy,ilayn/scipy,endolith/scipy,endolith/scipy,WarrenWeckesser/scipy,anntzer/scipy,mdhaber/scipy,ilayn/scipy,mdhaber/scipy,mdhaber/scipy,Stefan-Endres/scipy,mdhaber/scipy,anntzer/scipy,mdhaber/scipy,anntzer/scipy,scipy/scipy,endolith/scipy