gh-94808: Improve coverage of dictresize

[tqxia]

Try to improve test coverage for Objects/dictobject.c, adding the case "converting a split table into a generic combined table".

Code covered:

cpython/Objects/dictobject.c

Lines 1439 to 1452 in 894f2c3

	if (mp->ma_keys->dk_kind == DICT_KEYS_GENERAL) {
	// split -> generic
	PyDictKeyEntry *newentries = DK_ENTRIES(mp->ma_keys);
	for (Py_ssize_t i = 0; i < numentries; i++) {
	int index = get_index_from_order(mp, i);
	PyDictUnicodeEntry *ep = &oldentries[index];
	assert(oldvalues->values[index] != NULL);
	newentries[i].me_key = Py_NewRef(ep->me_key);
	newentries[i].me_hash = unicode_get_hash(ep->me_key);
	newentries[i].me_value = oldvalues->values[index];
	}
	build_indices_generic(mp->ma_keys, newentries, numentries);
	}

Issue:
#94808

• Issue: Metabug: Improving C-level coverage #94808

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