ci: Update reference commit for ABI check for 1.15 branch (#2059)

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

.github/workflows/ci.yml

@@ -336,7 +336,7 @@ jobs:
             fmt_ver: 10.1.1
             pybind11_ver: v2.10.0
             skip_tests: 1
-            abi_check: e3aa2cf5a17a59e906c7125ff8d546b1561e812f
+            abi_check: 89c8f639207fefdf5d4271a418ffe696eab5a2a2
             setenvs: export OSL_CMAKE_FLAGS="-DOSL_BUILD_TESTS=0 -DBUILD_TESTING=OFF -DUSE_QT=0"
                             OPENIMAGEIO_CMAKE_FLAGS="-DUSE_PYTHON=0"
                             CMAKE_BUILD_TYPE=RelWithDebInfo