ci(workflows): update .github.worklows/pr.yaml to use single process in regression test

Author: harryswift01

.github/workflows/pr.yaml

@@ -111,7 +111,7 @@ jobs:
           python -m pytest tests/regression \
             -m "not slow" \
             --dist=loadscope \
-            -n auto \
+            -n 1 \
             -k "${{ matrix.system }}" \
             -vv \
             --durations=20