fix(migrations): work around GinIndex+OpClass codegen regression in Django 5.x

[cmorinupgrade]

Problem

GinIndex(OpClass(Upper(field), name="gin_trgm_ops")) generates invalid SQL under Django 5.x. The operator class ends up inside the expression parens instead of after them:

-- Generated (broken):
CREATE INDEX ... USING gin ((UPPER("name") gin_trgm_ops))

-- Correct:
CREATE INDEX ... USING gin ((UPPER("name")) gin_trgm_ops)

PostgreSQL rejects this with syntax error at or near "gin_trgm_ops", causing the worker to crash-loop on startup when it tries to run migrations.

Two migrations are affected:

• core/0056_branch_name_trgm_idx
• core/0080_repository_repos_name_trgm_idx

Both were generated against Django 4.2 and worked fine then, but fail on Django 5.x.

Fix

Replace RiskyAddIndex with SeparateDatabaseAndState:

• database_operations: RiskyRunSQL with the correct hardcoded SQL (preserves the risky-skip behaviour via SKIP_RISKY_MIGRATION_STEPS)
• state_operations: plain AddIndex to keep Django's model state in sync

The SQL used is exactly what the migration docstrings already document as the intended DDL. IF NOT EXISTS makes it safe to re-run.

Testing

Verified against PostgreSQL 14 with Django 5.x — migrations apply cleanly.

---

Note

Medium Risk
Touches production database migrations by replacing ORM-generated index DDL with raw RunSQL, so mistakes could break migration application or leave schema/state mismatched, though the change is limited to two index creations and uses IF NOT EXISTS/reversible SQL.

Overview
Works around a Django 5.x SQL generation regression for GinIndex(OpClass(...)) by changing two trigram index migrations to use SeparateDatabaseAndState.

The DB step now runs explicit CREATE INDEX IF NOT EXISTS ... gin_trgm_ops via RiskyRunSQL (preserving SKIP_RISKY_MIGRATION_STEPS behavior), while the migration state still records the corresponding AddIndex so Django’s model state remains consistent.

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