fix(operations): Set alter_async=0 when dropping an index asynchronously

[phacops]

No description provided.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
1155	1	1154	2

View the top 1 failed tests by shortest run time

tests.migrations.test_operations test_drop_index_async

Stack Traces | 0.003s run time

Traceback (most recent call last):
  File ".../tests/migrations/test_operations.py", line 175, in test_drop_index_async
    assert (
AssertionError: assert ('ALTER TABLE test_table DROP INDEX IF EXISTS index_1 SETTINGS '\n 'mutations_sync=0, alter_sync=0;') == 'ALTER TABLE test_table DROP INDEX IF EXISTS index_1 SETTINGS mutations_sync=0;'
  - ALTER TABLE test_table DROP INDEX IF EXISTS index_1 SETTINGS mutations_sync=0;
  + ALTER TABLE test_table DROP INDEX IF EXISTS index_1 SETTINGS mutations_sync=0, alter_sync=0;
  ?                                                                              ++++++++++++++

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[getsentry-bot]

PR reverted: 4b5d202