Add Alpine 3.20 to OS testing matrix

[twz123]

Is your feature request related to a problem? Please describe.

Alpine 3.20 isn't currently tested in the OS testing matrix.

Describe the solution you would like

Add it to the matrix.

Describe alternatives you've considered

No response

Additional context

I've had problems getting SSH logins to work back in the day, that's why it hasn't been added until now. Probably just needs the right config settings.

[kke]

An image will be available at quay once footloose fork release is rolled out.

[twz123]

Bump to 3.20 :upside_down_face: