ci(workflows): include parallel execution for .github/workflows/pr.yaml

Author: harryswift01

.github/workflows/pr.yaml

@@ -106,12 +106,13 @@ jobs:
           python -m pip install --upgrade pip
           python -m pip install -e .[testing]
 
-      - name: Run fast regression tests (sequential for determinism)
+      - name: Run fast regression tests
         run: |
           python -m pytest tests/regression \
             -m "not slow" \
             -k "${{ matrix.system }}" \
-            -n 0 \
+            --dist=loadscope \
+            -n auto \
             -vv \
             --durations=20