flatpak: clear GDK_PIXBUF_MODULE_FILE

GDK_PIXBUF_MODULE_FILE is often set to a nix store path not available in a app
sandbox. This can cause some apps to fail launching, simply reset this env var
when running applications.

fixes https://github.com/NixOS/nixpkgs/issues/53441

pkgs/development/libraries/flatpak/default.nix

@@ -32,6 +32,7 @@ stdenv.mkDerivation rec {
     # patch taken from gtk_doc
     ./respect-xml-catalog-files-var.patch
     ./use-flatpak-from-path.patch
+    ./unset-env-vars.patch
   ];
 
   nativeBuildInputs = [

pkgs/development/libraries/flatpak/unset-env-vars.patch

@@ -0,0 +1,10 @@
+--- a/common/flatpak-run.c
++++ b/common/flatpak-run.c
+@@ -1192,6 +1192,7 @@ static const ExportData default_exports[] = {
+   {"PERLLIB", NULL},
+   {"PERL5LIB", NULL},
+   {"XCURSOR_PATH", NULL},
++  {"GDK_PIXBUF_MODULE_FILE", NULL},
+ };
+ 
+ static const ExportData no_ld_so_cache_exports[] = {