add github actions tests

[ericchiang]

Was chatting with @brandonweeks who mentioned go-tpm uses a different CI and expressed interest in github actions.

[chrisfenner]

@josephlr @alexmwu do either of you have context on why the current CI uses Cirrus instead of GH Actions?

[alexmwu]

@josephlr @alexmwu do either of you have context on why the current CI uses Cirrus instead of GH Actions?

Joe introduced this to both go-tpm-tools and go-tpm: google/go-tpm-tools#39, #126.

go-tpm-tools has since migrated to GH Actions (google/go-tpm-tools#135), so I don't see any special reason to use Cirrus CI. I don't have additional context and would just be guessing :).