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There are likely 1 of 3 things going on here:

Something from a previous build has been cached and is causing issues. To clean your colcon workspace, cd to the base of the workspace (above the src folder), and run rm -rf install/ build/ log/, then re-run the colcon command.
An incompatibility with the version of Google's Protocol Buffers that you have installed. If you installed them from source, go to the source folder and run sudo make uninstall and then try reinstalling with the command sudo apt install --reinstall protobuf-compiler protobuf-c-compiler libprotoc-dev libprobuf-dev.
An incompatibility with the version of Gazebo that you have installed. Did you install it from source? If so, you'll have to manually remove it (generally sudo make uninstall in the source code folder) and re-install it from the repositories (sudo apt install gazebo9).