Flutter 3.27 changed Overlay layout: an Overlay given infinite
height constraints now requires at least one OverlayEntry with
`canSizeOverlay: true` to delegate sizing, otherwise the entire
golden suite throws "Overlay was given infinite constraints" before
any test can render.
Marking the harness's only entry as size-determining is the minimal
fix — keeps the existing MediaQuery-driven layout shape intact and
unblocks every widget/golden test that uses `harness()`.
Co-Authored-By: Claude <noreply@anthropic.com>
jpmschweitzerandClaude
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