replace 512 bit dh key with a 2014 bit one (closes #23844)

Patch by Cédric Krier.

Lib/test/dh1024.pem

+-----BEGIN DH PARAMETERS-----
+MIGHAoGBAIbzw1s9CT8SV5yv6L7esdAdZYZjPi3qWFs61CYTFFQnf2s/d09NYaJt
+rrvJhIzWavqnue71qXCf83/J3nz3FEwUU/L0mGyheVbsSHiI64wUo3u50wK5Igo0
+RNs/LD0irs7m0icZ//hijafTU+JOBiuA8zMI+oZfU7BGuc9XrUprAgEC
+-----END DH PARAMETERS-----
+
+Generated with: openssl dhparam -out dh1024.pem  1024

Lib/test/dh512.pem

------BEGIN DH PARAMETERS-----
-MEYCQQD1Kv884bEpQBgRjXyEpwpy1obEAxnIByl6ypUM2Zafq9AKUJsCRtMIPWak
-XUGfnHy9iUsiGSa6q6Jew1XpKgVfAgEC
------END DH PARAMETERS-----
-
-These are the 512 bit DH parameters from "Assigned Number for SKIP Protocols"
-(http://www.skip-vpn.org/spec/numbers.html).
-See there for how they were generated.
-Note that g is not a generator, but this is not a problem since p is a safe prime.

Lib/test/test_ssl.py

@@ -64,7 +64,7 @@ BADKEY = data_file("badkey.pem")
 NOKIACERT = data_file("nokia.pem")
 NULLBYTECERT = data_file("nullbytecert.pem")
 
-DHFILE = data_file("dh512.pem")
+DHFILE = data_file("dh1024.pem")
 BYTES_DHFILE = os.fsencode(DHFILE)