Werk #16357: Check certificates: Fix checking of common name of issuer

The active certificate check (configured via the ruleset Check certificates) did not check the common name (CN) of the certificate issuer correctly:

• If only the checking of the issuer CN was activated, the CN of the subject was checked instead.
• If both the checking of the issuer and the subject CN where activated, the active check crashed with\ error: the argument '--subject-cn \<SUBJECT_CN>' cannot be used multiple times.

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