pythongh-122420: Fix accounting for immortal interned strings in refleak.py (pythonGH-122421)

The `_PyUnicode_Intern*` functions already adjust the total refcount, so
we don't want to readjust it in refleak.py.

Author: colesbury

Lib/test/libregrtest/refleak.py

@@ -145,7 +145,7 @@ def get_pooled_int(value):
             # Use an internal-only keyword argument that mypy doesn't know yet
             _only_immortal=True)  # type: ignore[call-arg]
         alloc_after = getallocatedblocks() - interned_immortal_after
-        rc_after = gettotalrefcount() - interned_immortal_after * 2
+        rc_after = gettotalrefcount()
         fd_after = fd_count()
 
         rc_deltas[i] = get_pooled_int(rc_after - rc_before)