Update ruby and mmtk-core repos revisions

The Ruby upstream removed the `v1`, `v2` and `v3` arguments from the
`newobj_of` function, so it is no longer `newobj_of`'s responsibility to
initialize those fields.  We made changes accordingly.

`rb_imemo_tmpbuf_auto_free_pointer` was also removed in favor for
`rb_imemo_tmpbuf_new`.

Author: wks

mmtk/Cargo.lock

@@ -37,7 +37,7 @@ features = ["is_mmtk_object", "object_pinning", "sticky_immix_non_moving_nursery
 
 # Uncomment the following lines to use mmtk-core from the official repository.
 git = "https://github.com/mmtk/mmtk-core.git"
-rev = "ef153615d115edf196c0df2029e4340468276372"
+rev = "27b4521ca73c2addbafe7ccf374c607d61f3ba51"
 
 # Uncomment the following line to use mmtk-core from a local repository.
 #path = "../../mmtk-core"