[ruby/mmtk] test_finalize is in TestObjectSpace not TestObjSpace

These filenames are passed into test classes, and the tests we're trying
to exclude exist in TestObjectSpace in the Ruby repo, not TestObjSpace

ruby/mmtk@195728dc8c

Author: eightbitraptor

test/.excludes-mmtk/TestObjSpace.rb

@@ -1,4 +1,3 @@
 exclude(:test_dump_all_full, "testing behaviour specific to default GC")
 exclude(:test_dump_flag_age, "testing behaviour specific to default GC")
 exclude(:test_dump_flags, "testing behaviour specific to default GC")
-exclude(:test_finalizer, "times out in debug mode on Ubuntu")

test/.excludes-mmtk/TestObjectSpace.rb

@@ -0,0 +1 @@
+exclude(:test_finalizer, "times out in debug mode on Ubuntu")