Add `meetup-mf2` tag to meetup-mf2 announce post

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Author's Checklist

• I have added appropriate tags to the article
  • I have tagged nablopomo / blogumentation appropriately
• I have added a series if appropriate
• I have update the article's commit date with the publish date
• I have checked the post for spelling and grammar
• I have added an appropriate post image to the metadata
• I have verified that any relevant issues are closed / referenced
• I have verified that this Merge Request is labelled appropriately