👩‍🌾 [ros2] Fix clang warning about hidden overloads

[chapulina]

Clang is overly cautions about virtual overloads. After #195 was merged, we started getting this warning in the macOS nightlies:

01:56:54 In file included from /Users/osrf/jenkins-agent/workspace/nightly_osx_release/ws/src/ros-perception/image_common/image_transport/src/manifest.cpp:38:
01:56:54 /Users/osrf/jenkins-agent/workspace/nightly_osx_release/ws/src/ros-perception/image_common/image_transport/include/image_transport/raw_subscriber.hpp:73:8: warning: 'image_transport::RawSubscriber::subscribeImpl' hides overloaded virtual function [-Woverloaded-virtual]
01:56:54   void subscribeImpl(
01:56:54        ^
01:56:54 /Users/osrf/jenkins-agent/workspace/nightly_osx_release/ws/src/ros-perception/image_common/image_transport/include/image_transport/simple_subscriber_plugin.hpp:115:8: note: hidden overloaded virtual function 'image_transport::SimpleSubscriberPlugin<sensor_msgs::msg::Image_<std::__1::allocator<void> > >::subscribeImpl' declared here: different number of parameters (4 vs 5)
01:56:54   void subscribeImpl(
01:56:54        ^
01:56:54 1 warning generated.

I tested locally on Ubuntu Focal with clang 10 that adding this line gives clang some peace of mind.

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https://github.com/osrf/buildfarmer/issues/207

[ivanpauno]

LGTM

[chapulina]

Can we get this in before the next nightly, @mjcarroll ? Thanks!

[clalancette]

Here's CI for this:

• Linux
• Linux-aarch64
• macOS
• Windows

[clalancette]

OK, CI is green here. I'm going to go ahead and merge this one to try and make our nightly CI happier.