Use multiple threads in CI

Author: JamesWrigley

.github/workflows/ci.yml

@@ -44,6 +44,7 @@ jobs:
       - uses: julia-actions/julia-runtest@v1
         env:
           JULIA_DISTRIBUTED_TESTING_STANDALONE: 1
+          JULIA_NUM_THREADS: 4
       - uses: julia-actions/julia-processcoverage@v1
       - uses: codecov/codecov-action@v5
         with: