Add more tests for the django-firebird driver

[vasiliy-yashkov]

A limited number of tests are currently in the django-firebird driver. Current driver test suite.
So not all Django features are tested with the driver. More tests should be added. The tests can be found in the Django repository.
The current tests should be updated first:

• Compare with the tests in the Django repository
• If there are changes in Django tests, add them to the existing driver tests
• Check the results of the updated tests
• Successful updated tests should be added to the django-firebird/tree/master/tests/ directory

If the updated tests failed, ensure that they are correct, and in case of driver errors - create appropriate issues in the driver project

The test database is created with the command:
python ./django-firebird/tests/test_main/manage.py migrate
The tests are run with the command
python ./django-firebird/tests/test_main/manage.py test --keepdb
When running tests, the --debug-mode parameter can be added for detailed output of query information.