Race between datachecksum enablement and create table with the file_copy strategy

Hello

There's a small race window between enabling data checksums and
creating a new database with the file_copy strategy:

Create database checks for in progress data checksums before it
inserts a new row into pg_database. If the data checksum worker starts
in that window, it can miss the new database completely and skip
generating its checksums.

See the attached patch and test case using a new injection point.