Fix double escaping in sigma_util causing yaml.parser.ParserError

[lo-chr]

This PR fixes the issue #3027, by simply passing the text of a sigma rule (rule_text instead of it's already escaped version doc) to sigmatools. sigmatools does the parsing and escaping of yaml by itself.

yaml.safe_load_all is still used for yaml-parsing (making sure, that the format is right) within this function, before calling the sigmatools library.

Like mentioned in the issue, the previous version led to ParserErrors, due to "double escaping" via yaml.safe_load_all in specific cases.

The PR also fixes one sigma_util.py test, which was failing mistakenly.

Checks

• All tests succeed.
• Unit tests added.

Closing issues
closes #3027

[jkppr]

Thanks @lo-chr for raising an issue and also providing a PR to fix it. Much appreciated.

The PR looks good. We will merge it before the next release.