BUG: fix system python dependency

[alexrockhill]

From testing, this was actually using the system-wide python install so probably should set up its own for a better config.

[YuriiMotov]

@alexrockhill, thanks for interest in this project!

The re-actors/alls-green cation only has standard dependencies and doesn't have any specific requirements on Python version.
Also, current implementation is inline with the official example.

Please, explain why you think this is important.
Installing Python will increase execution time. Do we need this?

[alexrockhill]

I ran this on a local runner without a system wide python installation and it failed because all-greens calls a plain python command within it.

[YuriiMotov]

I ran this on a local runner without a system wide python installation and it failed because all-greens calls a plain python command within it.

Then I would make this step conditional (if no Python 3 installed - install)

[stevleibelt]

@YuriiMotov how important is execution/build time compared to "comes with all batteries included"?

The less external and uncontrollable dependencies, the better and streamlined the result, or?