[3.12] gh-108843: fix ast.unparse for f-string with many quotes (GH-108981) (#109541)

gh-108843: fix ast.unparse for f-string with many quotes (GH-108981)
(cherry picked from commit 23f9f6f46454455bc6015e83ae5b5e946dae7698)

Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>