gitea: mark as broken on darwin

Build is currently failing:

```
/nix/store/za0pnll14dv61b124n6xxnjapd150lcr-go-1.19.4/share/go/pkg/tool/darwin_amd64/link: running clang failed: exit status 1
Undefined symbols for architecture x86_64:
  "_pam_start_confdir", referenced from:
      __cgo_897673d6bfaf_Cfunc_pam_start_confdir in 000032.o
      _check_pam_start_confdir in 000033.o
     (maybe you meant: _check_pam_start_confdir, __cgo_897673d6bfaf_Cfunc_check_pam_start_confdir , __cgo_897673d6bfaf_Cfunc_pam_start_confdir )
ld: symbol(s) not found for architecture x86_64
clang-11: error: linker command failed with exit code 1 (use -v to see invocation)
error: builder for '/nix/store/zqr2xx5a66km81m8av714sm45gy3ym0g-gitea-1.18.0.drv' failed with exit code 1;
```

pkgs/applications/version-management/gitea/default.nix

@@ -1,4 +1,5 @@
 { lib
+, stdenv
 , buildGoPackage
 , fetchurl
 , makeWrapper
@@ -68,5 +69,6 @@ buildGoPackage rec {
     homepage = "https://gitea.io";
     license = licenses.mit;
     maintainers = with maintainers; [ disassembler kolaente ma27 techknowlogick ];
+    broken = stdenv.isDarwin;
   };
 }