docs: record ArchRenderSceneTests as a fourth member of the #250 flake family

TransformUpdateBatch_ReusesRetainedStorage failed in two of six consecutive
whole-suite Release runs on a docs-only tree during Campaign V slice V7, and
passed 12/12 with its class run alone. Its assertion is the same shape as the
three already listed -- a GC.GetAllocatedBytesForCurrentThread() delta asserted
equal to zero across a warmed call -- so it is the known family rather than a new
defect. Recorded rather than re-investigated, which is the whole point of the
issue.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/ISSUES.md

@@ -248,6 +248,13 @@ tree:
   bytes against an expected 0, on a diff that touches only GLSL and the terrain
   renderer's uniform plumbing. It passed in isolation and in four other full
   runs of the same binary, so it is the same class rather than a new defect.)
+- `AcDream.App.Tests.Rendering.ArchRenderSceneTests.TransformUpdateBatch_ReusesRetainedStorage`
+  (added 2026-07-28 during Campaign V slice V7, on a docs-only tree. Two of six
+  consecutive whole-suite Release runs failed on it and nothing else; the class
+  passes 12/12 in isolation. Its assertion is the same shape as the others —
+  `GC.GetAllocatedBytesForCurrentThread()` delta across `scene.Apply(updates)`
+  asserted equal to zero — so it is a fourth member of this family, not a new
+  defect. Recorded so the next reader does not re-investigate it.)
 
 Measured over six consecutive Release runs of the App suite on an unmodified
 tree: four passed 3,846/3, and two failed with exactly one failure — a different