Set permissions to github workflows

[joycebrum]

Changes

Closes #411

• set permission to build.yml to contents read. Success run example: https://github.com/joycebrum/x86_64/actions/runs/4451339527
• set top level permission of release.yml to contents: read and grant contents: write on the job level. Considering the parmission to read on crates, I could not test it completely (although it had run with success on my fork). But considering that the GITHUB_TOKEN would basically be used to the POST on refs, the contents: write is enough.

Thanks and let me know if I missed anything.

[josephlr]

This looks reasonable. The only github permission needed for the release script is to tag the release. It seems like actions don't support restricting a token to specific content APIs, so we have to allow "write" for all content. This seems fine though.

We will see if this break stuff on the next release, but it shouldn't.

Thanks for the contribution.