maintainers: add bjsowa

maintainers/maintainer-list.nix

···
     githubId = 133602;
     name = "Bjørn Forsman";
   };
+  bjsowa = {
+    email = "[e-mail]";
+    github = "bjsowa";
+    githubId = 23124539;
+    name = "Błażej Sowa";
+  };
   bkchr = {
     email = "[e-mail]";
     github = "bkchr";