cairo: pull upstream fix for grayscale aliasing bug

It's a cairo part of the fix for issue #185385 reported by @tobiasBora.

pkgs/development/libraries/cairo/default.nix

@@ -62,6 +62,15 @@ in stdenv.mkDerivation rec {
       url = "https://gitlab.freedesktop.org/cairo/cairo/-/commit/e22d7212acb454daccc088619ee147af03883974.diff";
       sha256 = "sha256-8G98nsPz3MLEWPDX9F0jKgXC4hC4NNdFQLSpmW3ay2s=";
     })
+
+    # Fix unexpected color addition on grayscale images (usually text).
+    # Upstream fix: https://gitlab.freedesktop.org/cairo/cairo/-/merge_requests/114
+    # Can be removed after 1.18 release
+    (fetchpatch {
+      name = "fix-grayscale-anialias.patch";
+      url = "https://gitlab.freedesktop.org/cairo/cairo/-/commit/4f4d89506f58a64b4829b1bb239bab9e46d63727.diff";
+      sha256 = "sha256-mbTg67e7APfdELsuMAgXdY3xokWbGtHF7VDD5UyYqKM=";
+    })
   ];
 
   outputs = [ "out" "dev" "devdoc" ];