.github: avoid running tests in parallel

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

.github/workflows/build.yml

@@ -60,7 +60,7 @@ jobs:
           /tmp/sbin/initctl -h
       - name: Run Unit Tests
         run: |
-          make check || (cat test/test-suite.log; false)
+          make -j1 check || (cat test/test-suite.log; false)
       - name: Upload Test Results
         uses: actions/upload-artifact@v2
         with: