Assert WikiPage::Meta event has no personal_namespace_id

What does this MR do and why?

Assert WikiPage::Meta event has no personal_namespace_id

We add this check to create assurance that there is no more overlapping sharding keys being created in the case of group wikis

From #598786 (comment 3448032800), we previously had a bug which created events with both group_id and personal_namespace_id. This has been since fixed.

References

Related to #598786

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Before	After

How to set up and validate locally

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