tests: verify that 'certtool -i --outder' does not output text
A common regression in the past, was certtool outputting text while writing raw DER data. Ensure that the certificate-info option does not regress.
Checklist
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Test suite updated with negative tests
Reviewer's checklist:
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Any issues marked for closing are addressed -
There is a test suite reasonably covering new functionality or modifications -
Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTION.md
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This feature/change has adequate documentation added -
No obvious mistakes in the code