Playground: correct excludeFromAutomaticTesting reasons (texture-format, GPU-particle, remote-asset tests)

Replace stale/generic exclude reasons with the verbatim runtime error each
test actually hits on Babylon Native, re-verified on a fresh master build:

- Texture-format tests (#1609 family): RuntimeError: Unsupported texture
  format or type ... instead of a pixel-diff label.
- GPU-particle tests: the verbatim TypeError/ReferenceError thrown before
  rendering (ARRAY_BUFFER, 'Image'), and reuse of the existing
  'Cubemap load not implemented on Babylon Native' convention.
- Remote-asset / misc tests: several were mislabeled as generic pixel-diff
  or crash; use the actual thrown error (Unable to load ... Unknown error
  opening URL for curl-reachable URLs, createObjectURL missing, OBJ
  'Out of stack space', cubemap load gap), or the measured pixel-diff.

Reason-string wording only; no test is enabled or disabled.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bkaradzic