Add a warning to the CSP validator for 'self' on script-src directives.

[underdarknl]

This adds a warning to the CSP validator for 'self' on script-src directives.

Code Checklist

• All the commits in this PR are properly PGP-signed and verified.
• This PR only contains functionality relevant to the issue; tickets have been created for newly discovered issues.
• I have written unit tests for the changes or fixes I made.
• For any non-trivial functionality, I have added integration and/or end-to-end tests.
• I have performed a self-review of my code and refactored it to the best of my abilities.

Communication

• I have informed others of any required .env changes files if required and changed the .env-dist accordingly.
• I have made corresponding changes to the documentation, if necessary.
• I have included comments in the code to elaborate on what is not self-evident from the code itself, including references to issues and discussions online, or implicit behavior of an interface.

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Checklist for code reviewers:

Copy-paste the checklist from the docs/source/templates folder into your comment.

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Checklist for QA:

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[ammar92]

Looks good to me; just revert the mentioned spelling mistake and the test has to be updated

[stephanie0x00]

Checklist for QA:

• I have checked out this branch, and successfully ran a fresh make reset.
• I confirmed that there are no unintended functional regressions in this branch:
  • I have managed to pass the onboarding flow
  • Objects and Findings are created properly
  • Tasks are created and completed properly
• I confirmed that the PR's advertised feature or hotfix works as intended.

What works:

Can confirm that the change is shown (item 4).

What doesn't work:

n/a

Bug or feature?:

n/a