Tweak workflows

[mdpiper]

This PR contains a set of minor modifications to the mcflugen/render-github-workflows branch.

• Combined install of the build and library requirements in the Test action
• Only apply flake8 and black to the package directory
• Changed job name in Black action to "format"
• Used "args" instead of "black_args" in Black action
• Updated status badges in README

[mdpiper]

@mcflugen You can choose whether to accept or ignore this PR.

[mdpiper]

@mcflugen Also, I used this to update pymt_prms_surface.

[mcflugen]

@mdpiper Looks good! Thanks. The only thing I would change is that I think we should run black on everything, not just the generated package.

[mdpiper]

@mcflugen OK, I'll revert that change.