Set MMTK_JULIA_DIR before run ffi check

Author: udesou

.github/workflows/binding-tests.yml

@@ -71,6 +71,7 @@ jobs:
         run: |
           ./.github/scripts/ci-ffi.sh
       - run: |
+          MMTK_JULIA_DIR=$(realpath $(dirname "$0"))/../mmtk-julia/mmtk-julia
           if ! git diff --exit-code $MMTK_JULIA_DIR/mmtk/src/julia_types.rs; then
             echo "Rust FFI bindings in \`julia_types.rs\` are outdated. Run \`make regen-bindgen-ffi\` from the mmtk-julia directory and make sure to include the updated file in the pull request."
             exit 1