Fix tests for GC compiled with MANUAL_VDB

Fix tests for GC compiled with MANUAL_VDB

* tests/disclaim_test.c (pair_dct, pair_new): Call
GC_end_stubborn_change(p) after writing the last pointer field of p.
* tests/test.c [!DBG_HDRS_ALL] (run_one_test): Likewise.
* tests/test.c (small_cons, small_cons_uncollectable, mktree,
typed_test): Call GC_END_STUBBORN_CHANGE(r) after writing the last
pointer field of r.
* tests/test.c [GC_GCJ_SUPPORT] (gcj_cons): Likewise.
* tests/test.c [!SMALL_CONFIG && !GC_DEBUG] (alloc8bytes): Likewise.