Update plugins-known-issues.md (All-in-One WP Migration section)

[jrannelv]

Updated wp-content/ai1vm-backups to wp-content/ai1wm-backups

Closes #

Summary

Doc Page Title - <Enter a one sentence summation of the pertinent changes (including not-yet-completed work) provided by this PR.>

Effect

The following changes are already committed:

Remaining Work and Prerequisites

The following changes still need to be completed:

• [ ] List any outstanding work here

Dependencies and Timing

• [ ] Other prerequisites that must be completed before merging this PR

Release:

• [ ] When ready
• [ ] After date: $DATE

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Post Launch

Do not remove - To be completed by the docs team upon merge:

• [ ] Redirect /old-path/ => /new-path/ (if applicable)
• [ ] Include/exclude pages ^ respectively within docs search service provider (if applicable)
• [ ] For Heroes - add a props post to the discussion board.
• [ ] Remove from the project board