The 1.19 release notes are missing a line item under Breaking Changes:
Below is the upstream release note for this change:
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The feature flag `disable-affinity-assistant` has been removed. Please use `coschedule` as a replacement. It was marked as deprecated in version v0.51 and has been completely removed in the current version. If you need to maintain the previous default behavior, set feature flag `coschedule` to `disabled`. For specific behavioral differences, please refer to: https://github.com/tektoncd/community/blob/main/teps/0135-coscheduling-pipelinerun-pods.md#tep-0135-coscheduling-pipelinerun-pods
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Note: The field is still accepted by the Operator and TektonConfig, but it no longer has any effect.