how should we enable staging

[jku]

So I'm looking at doing some final testing before enabling staging test by default (changing the default value of the action input) however...

I started thinking about how this goes in the future (assume we have many more tests that support testing on staging):

• do we need to enable xfail for staging but not for prod? Probably yes because both get run on the same action invocation
• we could invent a syntax of our own (xfail: "test_name@staging" or something) and handle that in conformance_xfail() fixture -- or add another input to the action like xfail_staging

Alternatively we might want to require running the action separately for staging: this makes it easy to manage the xfail lists separately.

[jku]

I think I kind of like the idea of separate action invocations: this also looks more meaningful on GitHub: "failure in Staging conformance" requires very different action from "failure in conformance"

I'll make a PR of this and will do some testing...