Fix netfx test runs (#36082)
Fix netfx test runs (#36082)

* Fix netfx test SDK tfm for new package version

* Add validation that we actually found assets in package to catch this early

* PR Feedback

ptoonen/corefx,ericstj/corefx,ptoonen/corefx,shimingsg/corefx,wtgodbe/corefx,BrennanConroy/corefx,ViktorHofer/corefx,BrennanConroy/corefx,shimingsg/corefx,ericstj/corefx,ericstj/corefx,wtgodbe/corefx,shimingsg/corefx,ptoonen/corefx,ViktorHofer/corefx,wtgodbe/corefx,ViktorHofer/corefx,wtgodbe/corefx,shimingsg/corefx,ericstj/corefx,ericstj/corefx,wtgodbe/corefx,shimingsg/corefx,shimingsg/corefx,ptoonen/corefx,shimingsg/corefx,ViktorHofer/corefx,ericstj/corefx,ViktorHofer/corefx,ptoonen/corefx,ViktorHofer/corefx,wtgodbe/corefx,ericstj/corefx,ptoonen/corefx,wtgodbe/corefx,ptoonen/corefx,BrennanConroy/corefx,ViktorHofer/corefx