[jsk_rqt_plugins] Fix yaml load in tabbed_button_general.py

[Kanazawanaoaki]

The #811 (#818) change was not applied to tabbed_button_general.py, so I added it.

When using PyYAML version 6.0 or later, the old way of writing yaml.load() causes an error. yaml/pyyaml#576

[k-okada]

thank you for PR, merged in #884, with test code. It also noted that if you have pyyaml > 6.0, then you have non-official pyyaml module in your environment, usualy it cause a lot of problem, so please be very careful.