Update collect_all_artifacts.sh to install mono for 20.04 instead of 16.04

PiperOrigin-RevId: 495394221

kokoro/release/collect_all_artifacts.sh

@@ -49,11 +49,10 @@ cp ${INPUT_ARTIFACTS_DIR}/build64/src/protoc protoc/macosx_x64/protoc
 
 # Install nuget (will also install  mono)
 # TODO(jtattermusch): use "mono:5.14" docker image instead so we don't have to apt-get install
+sudo apt update
+sudo apt install gnupg ca-certificates
 sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
-echo "deb https://download.mono-project.com/repo/ubuntu stable-xenial main" | sudo tee /etc/apt/sources.list.d/mono-official-stable.list
-# NVidia has stopped publishing Cuda packages for Ubuntu 16.04, so we need to
-# delete this file to allow the apt update to run successfully.
-sudo rm -f /etc/apt/sources.list.d/cuda.list
+echo "deb https://download.mono-project.com/repo/ubuntu stable-focal main" | sudo tee /etc/apt/sources.list.d/mono-official-stable.list
 sudo apt update
 sudo apt-get install -y nuget
 

src/file_lists.cmake

@@ -168,8 +168,8 @@ set(libprotobuf_hdrs
   ${protobuf_SOURCE_DIR}/src/google/protobuf/reflection_ops.h
   ${protobuf_SOURCE_DIR}/src/google/protobuf/repeated_field.h
   ${protobuf_SOURCE_DIR}/src/google/protobuf/repeated_ptr_field.h
-  ${protobuf_SOURCE_DIR}/src/google/protobuf/serial_arena.h
   ${protobuf_SOURCE_DIR}/src/google/protobuf/service.h
+  ${protobuf_SOURCE_DIR}/src/google/protobuf/serial_arena.h
   ${protobuf_SOURCE_DIR}/src/google/protobuf/stubs/callback.h
   ${protobuf_SOURCE_DIR}/src/google/protobuf/stubs/common.h
   ${protobuf_SOURCE_DIR}/src/google/protobuf/stubs/logging.h