[3.13] pythongh-118658: Modify cert generation script to extract cert3.pem (pythonGH-124598)

(cherry picked from commit 480354d)

Co-authored-by: Felix Fontein <[email protected]>

Author: felixfontein

Lib/test/certdata/cert3.pem

@@ -254,6 +254,8 @@ def print_cert(path):
         f.write(key)
         f.write(cert)
 
+    check_call(['openssl', 'x509', '-outform', 'pem', '-in', 'keycert3.pem', '-out', 'cert3.pem'])
+
     cert, key = make_cert_key('fakehostname', sign=True)
     with open('keycert4.pem', 'w') as f:
         f.write(key)