Ignore key up events in teleop_turtle_key on Windows

[hidmic]

Precisely what the title says. Without this, goals were sent twice, resulting in:

C:\opt\ros>ros2 run turtlesim turtlesim_node
[INFO] [1618522185.883591800] [turtlesim]: Starting turtlesim with node name /turtlesim
[INFO] [1618522185.899227100] [turtlesim]: Spawning turtle [turtle1] at x=[5.544445], y=[5.544445], theta=[0.000000]
[INFO] [1618522191.815428400] [turtlesim]: Rotation goal completed successfully
[INFO] [1618522191.878537900] [turtlesim]: Rotation goal completed successfully
[WARN] [1618522207.286362400] [turtlesim]: Rotation goal received before a previous goal finished. Aborting previous goal
[INFO] [1618522209.606408200] [turtlesim]: Rotation goal completed successfully

[ivanpauno]

Sounds reasonable to me.
I also think that getting the "previous goal canceled" message wasn't pretty confusing.

[sloretz]

I didn't try this locally, but it looks good to me!

[hidmic]

I didn't try this locally

I did.

Running Windows CI for completeness:

[hidmic]

Alright, going in.