dosbox-staging: pull upstream fixes for SDL2_net and SDL2_image headers

Without the change `dosbox-staging` fails to build as:

FAILED: src/dos/libdos.a.p/program_serial.cpp.o
g++ -Isrc/dos/libdos.a.p -Isrc/dos -I../src/dos -I../include -I. -I.. -Isrc/libs/ghc -I../src/libs/ghc -Isrc/libs/loguru -I../src/libs/loguru -I/nix/store/58cdrn1birpig59wqygva9cmsnxh7wwa-SDL2-2.26.4-dev/include -I/nix/store/58cdrn1birpig59wqygva9cmsnxh7wwa-SDL2-2.26.4-dev/include/SDL2 -I/nix/store/y8ab9wi9sldj6y7md833xkbppgimrs>
In file included from ../src/dos/../hardware/serialport/softmodem.h:30,
from ../src/dos/program_serial.cpp:27:
../src/dos/../hardware/serialport/misc_util.h:59:10: fatal error: SDL_net.h: No such file or directory
59 | #include <SDL_net.h>
| ^~~~~~~~~~~

pkgs/applications/emulators/dosbox-staging/default.nix

···
 { lib
 , stdenv
 , fetchFromGitHub
+, fetchpatch
 , SDL2
 , SDL2_image
 , SDL2_net
···
     hash = "sha256-I90poBeLSq1c8PXyjrx7/UcbfqFNnnNiXfJdWhLPGMc=";
   };
 
+  patches = [
+    # Pull missind SDL2_net dependency:
+    #   https://github.com/dosbox-staging/dosbox-staging/pull/2358
+    (fetchpatch {
+      name = "sdl2-net.patch";
+      url = "https://github.com/dosbox-staging/dosbox-staging/commit/1b02f187a39263f4b0285323dcfe184bccd749c2.patch";
+      hash = "sha256-Ev97xApInu6r5wvI9Q7FhkSXqtMW/rwJj48fExvqnT0=";
+    })
+
+    # Pull missing SDL2_image dependency:
+    #   https://github.com/dosbox-staging/dosbox-staging/pull/2239
+    (fetchpatch {
+      name = "sdl2-image.patch";
+      url = "https://github.com/dosbox-staging/dosbox-staging/commit/ca8b7a906d29a3f8ce956c4af7dc829a6ac3e229.patch";
+      hash = "sha256-WtTVSWWSlfXrdPVsnlDe4P5K/Fnj4QsOzx3Wo/Kusmg=";
+      includes = [ "src/gui/meson.build" ];
+    })
+  ];
+
   nativeBuildInputs = [
     copyDesktopItems
     gtest
···
     SDL2_image
     SDL2_net
     speexdsp
-  ];
-
-  env.NIX_CFLAGS_COMPILE = toString [
-    "-I${SDL2_image}/include/SDL2"
-    "-I${SDL2_net}/include/SDL2"
   ];
 
   desktopItems = [