gh-128058: Fix test_builtin ImmortalTests (#128068)

On 32-bit Free Threading systems, immortal reference count
is 5 << 28, instead of 7 << 28.

Co-authored-by: Peter Bierma <[email protected]>

Author: vstinner

Lib/test/test_builtin.py

@@ -2691,7 +2691,10 @@ def __del__(self):
 class ImmortalTests(unittest.TestCase):
 
     if sys.maxsize < (1 << 32):
-        IMMORTAL_REFCOUNT = 7 << 28
+        if support.Py_GIL_DISABLED:
+            IMMORTAL_REFCOUNT = 5 << 28
+        else:
+            IMMORTAL_REFCOUNT = 7 << 28
     else:
         IMMORTAL_REFCOUNT = 3 << 30