TRY: back to 18.3 container, but use oiio main

Signed-off-by: Larry Gritz <[email protected]>

Author: lgritz

.github/workflows/ci.yml

@@ -665,8 +665,9 @@ jobs:
             # select the right runner type and whether tests are run.
             nametag: linux-optix-vfx2025
             runner: ${{ (github.repository_owner == 'AcademySoftwareFoundation' && 'ubuntu-20.04-gpu-t4-4c-16g-176h') || 'ubuntu-latest' }}
-            container: aswf/ci-osl:2025-clang18.2
+            container: aswf/ci-osl:2025-clang18.3
             cxx_std: 17
+            openimageio_ver: release
             python_ver: "3.11"
             pybind11_ver: v2.11.1
             simd: avx2,f16c