Rewrite time interval tests

[BuonOmo]

trafficstars

Pg time interval tests are using the keyword ago. Rewrite them without it.

• [ ] test_text_columns_are_limitless_the_upper_limit_is_one_GB
• [ ] test_data_type_of_oid_types
• [ ] test_update_oid
• [ ] test_data_type_of_time_types
• [ ] test_oid_values
• [ ] test_time_values
• [ ] test_update_large_time_in_seconds