Use threads on macOS

Author: seisman

.github/workflows/ci_tests_dev.yaml

@@ -98,7 +98,7 @@ jobs:
         run: |
           if [ "$RUNNER_OS" == "macOS" ]; then
              GMT_ENABLE_OPENMP=FALSE
-             GMT_USE_THREADS=FALSE
+             GMT_USE_THREADS=TRUE
           else
              GMT_ENABLE_OPENMP=TRUE
              GMT_USE_THREADS=TRUE