[3.13] gh-135386: Fix "unable to open database file" errors on readonly DB (GH-135566) (GH-138057)

Add immutable=1 flag for read-only SQLite access to avoid WAL/SHM errors on readonly DB.
(cherry picked from commit c0ae92b7c07d8146bbcc6ed5197f97a7a16efded)

Co-authored-by: General_K1ng <generak1ng0@gmail.com>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>