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-email.nix

@@ -6,6 +6,8 @@ with lib;
   imports = [ ../../accounts/email-test-accounts.nix ];
 
   config = {
+    accounts.email.accounts.hm-account.smtp.tls.certificatesFile =
+      "/etc/test/certificates.crt";
     programs.git = {
       enable = true;
       package = pkgs.gitMinimal;