maintainers: add tensor5

maintainers/maintainer-list.nix

···
     githubId = 2084639;
     name = "Manu";
   };
+  tensor5 = {
+    github = "tensor5";
+    githubId = 1545895;
+    matrix = "@tensor5:matrix.org";
+    name = "Nicola Squartini";
+  };
   teozkr = {
     email = "[e-mail]";
     github = "nightkr";