Use list instead of set for `options` (#62552)

src/sentry/options/defaults.py

@@ -843,7 +843,7 @@ register(
 register("attachment-cache.use-zstd", default=False, flags=FLAG_AUTOMATOR_MODIFIABLE)
 
 # Set of projects that will always store `EventAttachment` blobs directly.
-register("eventattachments.store-blobs.projects", default={}, flags=FLAG_AUTOMATOR_MODIFIABLE)
+register("eventattachments.store-blobs.projects", default=[], flags=FLAG_AUTOMATOR_MODIFIABLE)
 # Percentage sample rate for `EventAttachment`s that should use direct blob storage.
 register("eventattachments.store-blobs.sample-rate", default=0.0, flags=FLAG_AUTOMATOR_MODIFIABLE)