fix(sqlite): ignore choices-only alters (swev-id: django__django-15561)

[casey-brooks]

Problem

• Altering a CharField on SQLite that only changes choices currently triggers a table rebuild.
• These unnecessary rebuilds slow migrations and risk lock contention even though the schema is unchanged.

Fix

• Override _field_should_be_altered() in the SQLite schema editor to treat choices as a non-database attribute so choices-only updates are skipped.
• Add a regression test verifying alter_field() collects no SQL for a choices-only update.

Issue

• Closes SQLite: AlterField should be no-op for choices-only changes #499

Observed failure (pre-fix)

AssertionError: Lists differ: ['CREATE TABLE "new__backends_author" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "name" varchar(255) NOT NULL UNIQUE);', 'INSERT INTO "new__backends_author" ("id", "name") SELECT "id", "name" FROM "backends_author";', 'DROP TABLE "backends_author";', 'ALTER TABLE "new__backends_author" RENAME TO "backends_author";'] != []

CREATE TABLE "new__backends_author" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "name" varchar(255) NOT NULL UNIQUE);
INSERT INTO "new__backends_author" ("id", "name") SELECT "id", "name" FROM "backends_author";
DROP TABLE "backends_author";
ALTER TABLE "new__backends_author" RENAME TO "backends_author";

Traceback (pre-fix)

Traceback (most recent call last):
  File "django/tests/backends/sqlite/tests.py", line 214, in test_alter_field_choices_noop
    self.assertEqual(editor.collected_sql, [])
AssertionError: Lists differ: [...SQL statements...] != []

Reproduction

• ./runtests.py backends.sqlite -k test_alter_field_choices_noop
• python -m pytest -q django/tests/backends/sqlite/tests.py::SchemaTests::test_alter_field_choices_noop

Reference: internal task swev-id: django__django-15561.

[casey-brooks]

Local Validation

• PYTHONPATH=/workspace/django:$HOME/.nix-profile/lib/python3.11/site-packages DJANGO_SETTINGS_MODULE=tests.test_sqlite python3 tests/runtests.py backends.sqlite -k test_alter_field_choices_noop → 1 passed / 0 failed / 0 skipped
• PYTHONPATH=/workspace/django:$HOME/.nix-profile/lib/python3.11/site-packages flake8 django/db/backends/sqlite3/schema.py tests/backends/sqlite/tests.py → no lint errors

[noa-lucent]

Looks good to me. Thanks for scoping the change to SQLite and adding the regression test.