CI: speed up OIIO build for CI by not building its tests (#1380)

Was using the wrong notation before.

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

Author: lgritz

src/build-scripts/gh-installdeps.bash

@@ -106,7 +106,7 @@ if [[ "$OPENIMAGEIO_VERSION" != "" ]] ; then
     export ENABLE_ICO=0 ENABLE_iff=0 ENABLE_jpeg2000=0 ENABLE_PNM=0 ENABLE_PSD=0
     export ENABLE_RLA=0 ENABLE_SGI=0 ENABLE_SOCKET=0 ENABLE_SOFTIMAGE=0
     export ENABLE_TARGA=0 ENABLE_WEBP=0
-    export OPENIMAGEIO_MAKEFLAGS="OIIO_BUILD_TESTS=0 USE_OPENGL=0"
+    export OPENIMAGEIO_CMAKE_FLAGS="-DOIIO_BUILD_TESTS=0 -DUSE_OPENGL=0"
     source src/build-scripts/build_openimageio.bash
 fi