Reenable System.Runtime.CompilerServices.Unsafe-xunit test on 32bit

[akoeplinger]

It is disabled at the moment:

mono/scripts/ci/run-test-default.sh

Lines 90 to 91 in 1710dd7

	# Due to https://bugzilla.xamarin.com/show_bug.cgi?id=60865
	if [[ ${label} == *i386 ]] || [[ ${label} == w32 ]] || [[ ${label} == *armel ]] || [[ ${label} == *armhf ]]; then ${TESTCMD} --label=System.Runtime.CompilerServices.Unsafe-xunit --skip; else ${TESTCMD} --label=System.Runtime.CompilerServices.Unsafe-xunit --timeout=5m make -w -C mcs/class/System.Runtime.CompilerServices.Unsafe run-xunit-test; fi

https://bugzilla.xamarin.com/show_bug.cgi?id=60865 was fixed but to fix the test we need a corefx bump that includes the changes from #6129 (comment)

Reenable the test after corefx was bumped.