ARC: another critical bugfix; temporary tuples we introduce for tuple unpackaging are not owning the data

compiler/lowerings.nim

@@ -60,6 +60,7 @@ proc lowerTupleUnpacking*(g: ModuleGraph; n: PNode; owner: PSym): PNode =
   var temp = newSym(skTemp, getIdent(g.cache, genPrefix), owner, value.info, g.config.options)
   temp.typ = skipTypes(value.typ, abstractInst)
   incl(temp.flags, sfFromGeneric)
+  incl(temp.flags, sfCursor)
 
   var v = newNodeI(nkVarSection, value.info)
   let tempAsNode = newSymNode(temp)

tests/destructor/tmisc_destructors.nim

@@ -28,7 +28,7 @@ proc test(): auto =
 var (a, b, _) = test()
 
 doAssert assign_counter == 0
-doAssert sink_counter == 12 # + 3 because of the conservative tuple unpacking transformation
+doAssert sink_counter == 9 # XXX this is still silly and needs to be investigated
 
 # bug #11510
 proc main =