fix some DeprecationWarnings in python3.12

...\electrum\electrum\logging.py:137: DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).
...\electrum\electrum\x509.py:310: DeprecationWarning: datetime.datetime.utcfromtimestamp() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.fromtimestamp(timestamp, datetime.UTC).

electrum/x509.py

@@ -25,10 +25,9 @@
 
 import hashlib
 import time
-from datetime import datetime
 
 from . import util
-from .util import profiler
+from .util import profiler, timestamp_to_datetime
 from .logging import get_logger
 
 
@@ -307,7 +306,7 @@ class X509(object):
         if self.notBefore > now:
             raise CertificateError('Certificate has not entered its valid date range. (%s)' % self.get_common_name())
         if self.notAfter <= now:
-            dt = datetime.utcfromtimestamp(time.mktime(self.notAfter))
+            dt = timestamp_to_datetime(time.mktime(self.notAfter), utc=True)
             raise CertificateError(f'Certificate ({self.get_common_name()}) has expired (at {dt} UTC).')
 
     def getFingerprint(self):