Limit db name in tests to 63 chars

Postgres used to silently truncate the database name, but as of REL_17
it is no longer so.

In the tests we were using very long db names. After upgrading to 17,
test could no longer connect to the database.

The fix is to truncate db name that we're using in the tests to 63
chars.

https://github.com/postgres/postgres/commit/562bee0fc13dc95710b8db6a48edad2f3d052f2e