ci/eval/compare: manage the "by: package-maintainer" label

While OfBorg is still adding these, it takes a much longer time to do so
compared to the eval action. Since we're adding rebuild labels, I think
it'd be nice to just do it within the eval action.

ci/eval/compare/default.nix

@@ -10,6 +10,7 @@
   beforeResultDir,
   afterResultDir,
   touchedFilesJson,
+  githubAuthorId,
   byName ? false,
 }:
 let
@@ -114,7 +115,15 @@ let
           # Adds "10.rebuild-*-stdenv" label if the "stdenv" attribute was changed
           ++ lib.mapAttrsToList (kernel: _: "10.rebuild-${kernel}-stdenv") (
             lib.filterAttrs (_: kernelRebuilds: kernelRebuilds ? "stdenv") rebuildsByKernel
-          );
+          )
+          # Adds the "11.by: package-maintainer" label if all of the packages directly
+          # changed are maintained by the PR's author. (https://github.com/NixOS/ofborg/blob/df400f44502d4a4a80fa283d33f2e55a4e43ee90/ofborg/src/tagger.rs#L83-L88)
+          ++ lib.optional (
+            maintainers ? ${githubAuthorId}
+            && lib.all (lib.flip lib.elem maintainers.${githubAuthorId}) (
+              lib.flatten (lib.attrValues maintainers)
+            )
+          ) "11.by: package-maintainer";
       }
     );