Django creates the test database for Postgresql with incorrect sequences start values
If you don't recreate the db with every test, then you've have to reset the sequences yourself.
Also, I think that the sequence definition you've posted were found when inspecting the db after the tests run with a db tool. In that case, I think your db tool is presenting you the SQL to create the sequence as it is: after it's been used.
The fact that it doesn't happen on sqlite has to do with it using a in-memory db by default. Therefore, it's being re-created in every test run.