git: Add configured SSL certificate for SMTP (#1833)

If you have a custom SSL certificate configured for SMTP TLS, git should
use it.

tests/modules/programs/git/git-with-msmtp-expected.conf

@@ -2,6 +2,7 @@
 	from = "hm@example.org"
 	smtpEncryption = "tls"
 	smtpServer = "smtp.example.org"
+	smtpSslCertPath = "/etc/ssl/certs/ca-certificates.crt"
 	smtpUser = "home.manager.jr"
 
 [sendemail "hm@example.com"]