Parse All Top-Level GHA Constructs

[RobbieMcKinstry]

GHA Workflows have a well-defined schema. The schema consists of a number of top-level constructs: jobs, environment, etc. Once Punchcard can parse top-level constructs, all Workflow YAML files should be at least somewhat parsable, even if they don't get the details perfect.

This issue tracks the remaining work involved in parsing all top-level constructs.

• [x] name
• [x] run-name
• [x] on
  • [ ] workflow-call
  • [ ] schedule
  • [ ] workflow-dispatch
• [x] env
• [x] permissions
• [x] jobs
• [x] defaults
• [x] concurrency

env is an ordered map from strings to strings, making it simple to parse. jobs, on the other hand, have a large schema, requiring a lot of work. permissions will be easy to implement using an enum.

[RobbieMcKinstry]

Note: a number of the bugs in this implement can be fixed with https://serde.rs/enum-representations.html#untagged I'll have to come back to these in the future. For now, we'll soldier along until we find a workflow that doesn't parse correctly.