Add fallback for Certificate.not_valid_before/after_utc #5709

Job	Run time
Waiting for build / Waiting For Build	7m 38s
OCSP with self certificate verification test	8m 25s
Basic OCSP / Test	5m 8s
OCSP on separate instance / Test	4m 37s
OCSP clone / Test	9m 0s
OCSP with CMC / Test	4m 50s
OCSP with existing config / Test	5m 15s
OCSP with external certs / Test	4m 41s
OCSP with direct CRL publishing / Test	5m 53s
Standalone OCSP / Test	4m 0s
OCSP container / Test	6m 15s
OCSP with LDAP-based CRL publishing / Test	6m 38s
OCSP with HSM / Test	4m 36s
	1h 16m 56s

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