GitHub Workflows security hardening

[sashashura]

This PR adds explicit permissions section to workflows. This is a security best practice because by default workflows run with extended set of permissions (except from on: pull_request from external forks). By specifying any permission explicitly all others are set to none. By using the principle of least privilege the damage a compromised workflow can do (because of an injection or compromised third party tool or action) is restricted. It is recommended to have most strict permissions on the top level and grant write permissions on job level case by case.

[welcome[bot]]

Thanks for opening your first pull request in this repository! :v:

[sashashura]

Are we waiting for anything?

[ChristophWurst]

Green CI. Mind rebasing your branch to the latest master?

[sashashura]

Done.