[3.14] gh-145607: Ensure BIG_DATA has two compressed blocks in test_bz2 (GH-145730) (#145733)

gh-145607: Ensure BIG_DATA has two compressed blocks in test_bz2 (GH-145730)
(cherry picked from commit 19676e5fc28bdee8325a062a31ddeee60960cf75)

Co-authored-by: Emma Smith <emma@emmatyping.dev>