fix(code-review): add date_updated to update_fields

[srest2021]

followup to #106977

Add "date_updated" to update_fields when bulk creating repo settings. Otherwise the value will not update.

[sentry]

Bug: Adding date_updated to update_fields in bulk_create without explicitly setting its value will not update the timestamp due to how Django handles auto_now fields on conflict.
_{Severity: MEDIUM}

Suggested Fix

Before appending each RepositorySettings object to the settings_to_upsert list, explicitly set its date_updated attribute to the current time. For example: setting.date_updated = timezone.now().

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location:
src/sentry/integrations/api/endpoints/organization_repository_settings.py#L70-L73

Potential issue: The code adds `"date_updated"` to the `update_fields` list for a
`RepositorySettings.objects.bulk_create` call with `update_conflicts=True`. However, it
does not set a value for `date_updated` on the model instances. Django's `auto_now=True`
mechanism on a `DateTimeField` does not automatically update the timestamp during an
`INSERT ... ON CONFLICT DO UPDATE` operation when the field is specified in
`update_fields`. As a result, the `date_updated` field will either be set to `None` for
new records or retain its old value for existing records, instead of being updated to
the current time. This leads to incorrect timestamp data for repository settings
modifications.

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[srest2021]

It's true that doing a bulk create will not hit save() and therefore auto_now on date_updated won't run. However, when we add date_updated to update_fields without manually setting it to anything, it'll get set to db_default=Now() and override the old value thanks to update_conflicts=True.

[srest2021]

The issue is well-explained by this comment which I overlooked #106977 (comment)