Upgrade the copy of Protoc used on GitHub Actions.

Author: psobot

.github/workflows/python-package.yml

@@ -25,9 +25,9 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
-        # protobuf 3.6.1 or later is necessary
-        wget https://github.com/google/protobuf/releases/download/v3.6.1/protoc-3.6.1-linux-x86_64.zip
-        unzip protoc-3.6.1-linux-x86_64.zip -d protoc3
+        # protobuf 3.19.1 or later is necessary
+        wget https://github.com/google/protobuf/releases/download/v3.19.1/protoc-3.19.1-linux-x86_64.zip
+        unzip protoc-3.19.1-linux-x86_64.zip -d protoc3
         echo "::set-env name=PATH::$PATH:$PWD/protoc3/bin/"
         sudo apt-get install -qq libsnappy-dev
         python -m pip install --upgrade pip