tweak CI, including NUM_THREADS=2

Author: ablaom

.github/workflows/CI.yml

@@ -45,7 +45,11 @@ jobs:
             ${{ runner.os }}-
       - uses: julia-actions/julia-buildpkg@latest
       - uses: julia-actions/julia-runtest@latest
-      - uses: julia-actions/julia-uploadcodecov@v0.1
-        continue-on-error: true
+        env:
+          JULIA_NUM_THREADS: 2
+      - uses: julia-actions/julia-processcoverage@v1
+      - uses: codecov/codecov-action@v3
+        with:
+          file: lcov.info