Update 8.x to 8.19 in config

[colleenmcginnis]

The build is failing because repos that contain docs and code are changing their 8.x branch to 8.19. I don't expect this to pass on the first try, but I'll keep an eye on it as more repos make this change.

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[colleenmcginnis]

Not all repos are creating 8.19 branches yet so I'm not sure how to handle it when a repo with 8.x and a repo with 8.19 are used in the same book.

[lcawl]

Pre-approval once builds are green