keyboxd: Fix database schema migration.

* kbx/backend-sqlite.c (migrate_from_v1_to_v2): Explicitly name the
columns of the new table.

The problem was that I obviously tested only with an empty fingerprint
table or didn't noticed that error: "table fingerprint_new has 6
columns but 5 values were supplied". Fun with migration testing.

• GnuPG-bug-id: T7892
• Fixes-commit: 0cc7759ed5a3890b4e28563a6b5e97f3aa551530