opencore-amr: adjust homepage to have index-able URL

pkgs/by-name/op/opencore-amr/package.nix

···
   };
 
   meta = {
-    homepage = "https://opencore-amr.sourceforge.io/";
+    homepage = "https://sourceforge.net/projects/opencore-amr/";
     description = "Library of OpenCORE Framework implementation of Adaptive Multi Rate Narrowband and Wideband (AMR-NB and AMR-WB) speech codec.
     Library of VisualOn implementation of Adaptive Multi Rate Wideband (AMR-WB)";
     license = lib.licenses.asl20;