Fix schema order for published incidents

What does this MR do?

!30120 (closed) merged a migration which had several changes during review, including reordering columns. This got missed in db/structure.sql, so now db/structure.sql unfortunately has out-of-order columns relative to the migration.

This MR updates db/structure.sql to reflect the actual migration. See !29994 (comment 333453951).

Changes via:

$ rake db:migrate:down VERSION=20200416005331
== 20200416005331 CreateStatusPagePublishedIncidents: reverting ===============
-- drop_table(:status_page_published_incidents)
   -> 0.0027s
== 20200416005331 CreateStatusPagePublishedIncidents: reverted (0.0028s) ======

$ rake db:migrate
== 20200416005331 CreateStatusPagePublishedIncidents: migrating ===============
-- create_table(:status_page_published_incidents)
   -> 0.0105s
== 20200416005331 CreateStatusPagePublishedIncidents: migrated (0.0216s) ======

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Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
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• Style guides
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• [-] Separation of EE specific content

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• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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