maintainers: add zseri

maintainers/maintainer-list.nix

···
     github = "pulsation";
     githubId = 1838397;
   };
+  zseri = {
+    name = "zseri";
+    email = "[e-mail]";
+    github = "zseri";
+    githubId = 1618343;
+    keys = [{
+      longkeyid = "rsa4096/0x229E63AE5644A96D";
+      fingerprint = "7AFB C595 0D3A 77BD B00F  947B 229E 63AE 5644 A96D";
+    }];
+  };
   zupo = {
     name = "Nejc Zupan";
     email = "[e-mail]";