ci: Check whether test failures are caused by port exhaustion (#5938)

This change adds an extra step to the CI test job that outputs network info, which may allow us to confirm whether random test failures are caused by port exhaustion.

.github/workflows/reusable-test.yml

@@ -100,3 +100,12 @@ jobs:
               "$test_file"
             fi
           done
+
+      - name: Debug failure (Linux)
+        if: ${{ failure() && runner.os == 'Linux' && inputs.run_tests }}
+        shell: bash
+        run: |
+          echo "IPv4 local port range:"
+          cat /proc/sys/net/ipv4/ip_local_port_range
+          echo "Netstat:"
+          netstat -an