When merging CC certs, security level reports false mismatch

[J08nY]

Describe the bug
In the CC processing pipelines, the HTML and CSV certificates are merged. This merging detects when something is mismatched between two certs with shared digest. However, there is currently a false positive based on the security_level field. For one side the field is set() (empty set) and for the other it is {""} (set with empty string). This gets reported for most certificates, so something is likely wrong with the security level parsing.

2023-09-21 12:07:52,490 - sec_certs.sample.certificate - WARNING - When merging certificates with dgst fcc7abb7b11d12d4, the following mismatch occured: Attribute=security_level, self[security_level]={''}, other[security_level]=set()
2023-09-21 12:07:52,490 - sec_certs.sample.certificate - WARNING - When merging certificates with dgst 8298c7814b3b2860, the following mismatch occured: Attribute=security_level, self[security_level]={''}, other[security_level]=set()
2023-09-21 12:07:52,490 - sec_certs.sample.certificate - WARNING - When merging certificates with dgst 979e00ac7d3e229c, the following mismatch occured: Attribute=security_level, self[security_level]={''}, other[security_level]=set()

To Reproduce
Run sec-certs cc build.

Desktop (please complete the following information):
Commit 30f7475
Run time 21.09.2023