Bump psycopg2 from 2.8.3 to 2.8.4

Bumps [psycopg2](https://github.com/psycopg/psycopg2) from 2.8.3 to 2.8.4.
- [Release notes](https://github.com/psycopg/psycopg2/releases)
- [Changelog](https://github.com/psycopg/psycopg2/blob/master/NEWS)
- [Commits](https://github.com/psycopg/psycopg2/commits)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements_migrations.txt

 # Those dependencies are needed for the test_migrations.sh script
 PyMySQL==0.9.3
-psycopg2==2.8.3
+psycopg2==2.8.4