Turn CI runs as PR checks for merging

[juanmanso]

Description

After [tbd] and [tbd], our codebase is free of linting issues and CI is passing. So this task is for repo admins to turn on CI check for PRs

Accpetance criteria

• Failing CI runs block merge of PRs
• Properly formatted and linted code should not be blocked by CI to merge its PR

Related issues

• Related to Use Nox to improve DX by adding session based commands #103
• Related to Setup Black formatting and Flake8 linting #105
• Blocked by Add Nox for Black formatting and Flake8 linting on pre-commit & CI #106
• Blocked by Apply Flake8 linting feedback #107

[Luka-Loncar]

Wontfix