fix(model/featurestate): make environment not null

[gagantrivedi]

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Changes

Don't allow null value for environment field of feature state model.

Here is the sqlmigrate of the migration:

BEGIN;
--
-- Alter field environment on featurestate
--
SET CONSTRAINTS "features_featurestat_environment_id_c5882902_fk_environme" IMMEDIATE; ALTER TABLE "features_featurestate" DROP CONSTRAINT "features_featurestat_environment_id_c5882902_fk_environme";
ALTER TABLE "features_featurestate" ALTER COLUMN "environment_id" SET NOT NULL;
ALTER TABLE "features_featurestate" ADD CONSTRAINT "features_featurestat_environment_id_c5882902_fk_environme" FOREIGN KEY ("environment_id") REFERENCES "environments_environment" ("id") DEFERRABLE INITIALLY DEFERRED;
COMMIT;

How did you test this code?

Adds migration test

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Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (5b46cc0) 95.47% compared to head (28ee9cd) 95.48%.
Report is 11 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #2708    +/-   ##
========================================
  Coverage   95.47%   95.48%            
========================================
  Files         986      988     +2     
  Lines       27709    27810   +101     
========================================
+ Hits        26454    26553    +99     
- Misses       1255     1257     +2     

Files Changed	Coverage Δ
api/features/models.py	93.60% <ø> (+0.01%)	⬆️
...ions/0060_set_featurestate_environment_not_null.py	100.00% <100.00%> (ø)
api/tests/unit/features/test_migrations.py	100.00% <100.00%> (ø)

... and 9 files with indirect coverage changes

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[novakzaballa]

LGTM

[matthewelwell]

I don't know if it makes a difference, but the correct way to do this I think is: filter(environment__isnull=True). I think it's perhaps because in different database engines, it handles null differently.

[gagantrivedi]

Yeah, done