excel export: enhance handling of finding groups, better logging

[valentijnscholten]

Enhance logging for errors during Excel exports. Or rather they are warnings, so we log them at warning level from now on.

Inspired by #11911

Added later: Some more testing lead me to what I believe is a copy-and-paste error where get_foreign_keys() was not called.

So the PR now also fixes the conversion problem and outputs finding group values correctly:

fixes #10012

[dryrunsecurity]

This pull request introduces potential logging risks, including a debug log that might expose sensitive finding information and a reduction in error logging severity that could obscure important processing issues.

💭 Unconfirmed Findings (2)

Vulnerability	Potential Information Disclosure via Logging
Description	Debug log statement logs finding ID during processing, which could expose sensitive finding information if log files are not properly secured. This may lead to unintended information leakage.

Vulnerability	Reduced Error Visibility
Description	Error logging severity was changed from 'logger.error()' to 'logger.warning()', which reduces the visibility and severity of potential processing errors. This change may mask underlying issues in attribute handling and make troubleshooting more difficult.

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All finding details can be found in the DryRun Security Dashboard.

[mtesauro]

Approved