v0.25.0 compresses through compress_json, which switched from gzip to
zstd in 0.38.0 — the same release that added this migration. v0.38.0
decompressed with gzip and fell back to a raw UTF-8 decode, and both
fail on a zstd frame, so upgrading any database older than 0.25.0 has
died with UnicodeDecodeError since the migration shipped.
Reported with a fix by @omaer0 in #586.
