gh-134248 test_getallocatedblocks pre-check to ignore immortalized strings (#134871)

When sanity checking against gettotalrefcount(), we exclude the blocks for
immortalized strings since their references are not tracked/reported. This
now matches refleak.py's book-keeping using the same functions.

Author: tpburns

Lib/test/test_sys.py

@@ -1135,23 +1135,12 @@ def test_getallocatedblocks(self):
         b = sys.getallocatedblocks()
         self.assertLessEqual(b, a)
         try:
-            # While we could imagine a Python session where the number of
-            # multiple buffer objects would exceed the sharing of references,
-            # it is unlikely to happen in a normal test run.
-            #
-            # In free-threaded builds each code object owns an array of
-            # pointers to copies of the bytecode. When the number of
-            # code objects is a large fraction of the total number of
-            # references, this can cause the total number of allocated
-            # blocks to exceed the total number of references.
-            #
-            # For some reason, iOS seems to trigger the "unlikely to happen"
-            # case reliably under CI conditions. It's not clear why; but as
-            # this test is checking the behavior of getallocatedblock()
-            # under garbage collection, we can skip this pre-condition check
-            # for now. See GH-130384.
-            if not support.Py_GIL_DISABLED and not support.is_apple_mobile:
-                self.assertLess(a, sys.gettotalrefcount())
+            # The reported blocks will include immortalized strings, but the
+            # total ref count will not. This will sanity check that among all
+            # other objects (those eligible for garbage collection) there
+            # are more references being tracked than allocated blocks.
+            interned_immortal = sys.getunicodeinternedsize(_only_immortal=True)
+            self.assertLess(a - interned_immortal, sys.gettotalrefcount())
         except AttributeError:
             # gettotalrefcount() not available
             pass