bpo-46425: fix direct invocation of test_sqlite3

[sobolevn]

This fixes ./python.exe Lib/test/test_sqlite3/... tests.
Without this change it fails:

» ./python.exe Lib/test/test_sqlite3/test_transactions.py Traceback (most recent call last):
File "/Users/sobolev/Desktop/cpython/Lib/test/test_sqlite3/test_transactions.py", line 26, in <module>
from .test_dbapi import memory_database
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ImportError: attempted relative import with no known parent package

Refs #30666
CC @corona10 as my mentor.

https://bugs.python.org/issue46425

[erlend-aasland]

lgtm, thanks!

[erlend-aasland]

This should not be backported. The sqlite3 test suite has changed a lot since 3.10 and 3.9. I don't think this would apply cleanly at all. IMO, I don't think it is worth backporting it.