Enforce stricter merge restrictions

[RaulSMS]

I have relaxed the PR merged constrains due to the fact that we are refactoring structural test and code conventions tools.
We need speed in this phase until we can release a v1.0.0

For now:

• One single peer review
• Test on latest python version mandatory

Later we should

• Two mandatory reviews
• Enforce green test on all CIs scenarios

[RaulSMS]

In order to have a 10/10 score in https://github.com/RaulSMS/python-can-j1939/security/code-scanning/5 we need to:

Warn: required approving review count is 1 on branch 'master'
To pass Tier 4 and get a 9/10, Scorecard requires a minimum of 2 approving reviews before a PR can be merged. Since your rule only requires 1, it triggers a warning.

Warn: codeowners review is not required on branch 'master'
Tier 4 also mandates that you check the box "Require review from Code Owners" in your branch protection rules (which requires creating a .github/CODEOWNERS file if you don't have one).