fix: handle optional next update for CRL

[rudrakhp]

What type of PR is this?

fix: handle optional next update for crl

What this PR does / why we need it:
Allow valid CRLs with non-nil nextUpdate values. Note that only nextUpdate is optional while thisUpdate is mandatory according to RFC 5280:

CertificateList  ::=  SEQUENCE  {
        tbsCertList          TBSCertList,
        signatureAlgorithm   AlgorithmIdentifier,
        signatureValue       BIT STRING  }

   TBSCertList  ::=  SEQUENCE  {
        version                 Version OPTIONAL,
                                     -- if present, MUST be v2
        signature               AlgorithmIdentifier,
        issuer                  Name,
        thisUpdate              Time,
        nextUpdate              Time OPTIONAL,
        revokedCertificates     SEQUENCE OF SEQUENCE  {
             userCertificate         CertificateSerialNumber,
             revocationDate          Time,
             crlEntryExtensions      Extensions OPTIONAL
                                      -- if present, version MUST be v2
                                  }  OPTIONAL,
        crlExtensions           [0]  EXPLICIT Extensions OPTIONAL
                                      -- if present, version MUST be v2
                                  }

Which issue(s) this PR fixes:

Fixes #7391

Release Notes: No

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.33%. Comparing base (3ac9120) to head (63d590f).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7422      +/-   ##
==========================================
+ Coverage   72.31%   72.33%   +0.01%     
==========================================
  Files         231      231              
  Lines       33970    33970              
==========================================
+ Hits        24566    24572       +6     
+ Misses       7634     7629       -5     
+ Partials     1770     1769       -1     

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[rudrakhp]

/retest