[3.14] gh-134248 test_getallocatedblocks pre-check to ignore immortalized strings (GH-134871) (#135095)

gh-134248 test_getallocatedblocks pre-check to ignore immortalized strings (GH-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.
(cherry picked from commit 54ca55978e305ebb099d1b49633211597625bd52)

Co-authored-by: tpburns <trevorpburns@gmail.com>