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.

[codecov]

Codecov Report

Base: 76.66% // Head: 76.66% // No change to project coverage 👍

Coverage data is based on head (ed1157b) compared to base (a3fd3ca).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #233   +/-   ##
=======================================
  Coverage   76.66%   76.66%           
=======================================
  Files          10       10           
  Lines         360      360           
  Branches      112      112           
=======================================
  Hits          276      276           
  Misses         73       73           
  Partials       11       11           

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