add highs version requirements for pr workflow

.github/workflows/test_pr_and_main.yml

@@ -606,7 +606,7 @@ jobs:
       shell: bash
       run: |
         echo "NOTE: temporarily pinning to highspy pre-release for testing"
-        $PYTHON_EXE -m pip install --cache-dir cache/pip highspy==1.7.1.dev1 \
+        $PYTHON_EXE -m pip install --cache-dir cache/pip highspy>=1.7.1.dev1 \
             || echo "WARNING: highspy is not available"
 
     - name: Set up coverage tracking