Registry tool: compute conformance requires exact matches of spec mime types

[timburks]

Currently compute conformance will only run on specs whose mime types exactly match the mime types listed in the style guide. This can make linting fragile -- a style guide might include application/x.openapi+gzip;version=3 in its mime types and fail to match specs with any of these similar types:

• application/x.openapi+gzip;version=3.0.0
• application/x.openapi+gzip;version=3.0
• application/x.openapi;version=3

I think a reasonable solution to this would be to accept wildcards or regular expressions in the styleguide mime type list, but let's consider both of these possibilities and any other suggestions with mock style guides (in this thread) before making code changes.

[theganyo]

https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#filter-pattern-cheat-sheet