maintainers: add marcin-serwin

(cherry picked from commit f5a888c415c5e1e3347870c506e46f5a9bba9aa9)

maintainers/maintainer-list.nix

···
     githubId = 34819524;
     name = "Marcel";
   };
+  marcin-serwin = {
+    name = "Marcin Serwin";
+    github = "marcin-serwin";
+    githubId = 12128106;
+    email = "[e-mail]";
+    keys = [ { fingerprint = "F311 FA15 1A66 1875 0C4D  A88D 82F5 C70C DC49 FD1D"; } ];
+  };
   marcovergueira = {
     email = "[e-mail]";
     github = "marcovergueira";