更新ubuntu-20.04，18.04 github已经unsupported

actions/runner-images#6002

Author: SundoggyNew

.github/workflows/libxp2p_android_combine.yml

@@ -15,7 +15,7 @@ env:
 
 jobs:
   build-and-deploy:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
     - name: Checkout
       uses: actions/checkout@v2