ci: pkg config libdir fix (#4775)

This was causing the Rust bindings to fail because the pkgconfig was
pointing to a path that didn't exist (the libdir was the full root
appended to itself).

Signed-off-by: Scott Wilson <scott@propersquid.com>

Author: scott-wilson

src/build-scripts/ci-build.bash

@@ -37,7 +37,7 @@ cmake -S $OIIO_SRC_DIR -B $OIIO_BUILD_DIR -G "$CMAKE_GENERATOR" \
         -DCMAKE_PREFIX_PATH="$CMAKE_PREFIX_PATH" \
         -DCMAKE_INSTALL_PREFIX="$OpenImageIO_ROOT" \
         -DPYTHON_VERSION="$PYTHON_VERSION" \
-        -DCMAKE_INSTALL_LIBDIR="$OpenImageIO_ROOT/lib" \
+        -DCMAKE_INSTALL_LIBDIR="lib" \
         -DCMAKE_CXX_STANDARD="$CMAKE_CXX_STANDARD" \
         -DOIIO_DOWNLOAD_MISSING_TESTDATA=ON \
         -DEXTRA_CPP_ARGS="${OIIO_EXTRA_CPP_ARGS}" \