forgejo: fix applying of our `STATIC_ROOT_PATH` patch

This fixes an issue where running the forgejo package standalone,
without the use of our nixos/forgejo module, would try to use a
directory named `@data@` for its `STATIC_ROOT_PATH` assets.

This went unnoticed until now, because most users use the nixos/forgejo
module in which we explicitly set this option/setting/path to
`cfg.package.data` by default (`pkgs.forgejo.data`).

Also, this commit hard-copies the patch in question from gitea to our
nixpkgs derivation directory.

We decided a long time ago to part ways, and forgejo inheriting the
patch from gitea's drv directory puts strain on gitea.

So we don't do that anymore and instead maintain that patch ourselves
from now on.

Unfortunately, `substituteInPlace --subst-var` does not error, when the
substitution fails.

This would have prevented this issue from going unnoticed.

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

@@ -59,11 +59,11 @@ buildGoModule rec {
   buildInputs = lib.optional pamSupport pam;
 
   patches = [
-    ./../gitea/static-root-path.patch
+    ./static-root-path.patch
   ];
 
   postPatch = ''
-    substituteInPlace modules/setting/setting.go --subst-var data
+    substituteInPlace modules/setting/server.go --subst-var data
   '';
 
   tags = lib.optional pamSupport "pam"

pkgs/applications/version-management/forgejo/static-root-path.patch

@@ -0,0 +1,13 @@
+diff --git a/modules/setting/server.go b/modules/setting/server.go
+index 183906268..fa02e8915 100644
+--- a/modules/setting/server.go
++++ b/modules/setting/server.go
+@@ -319,7 +319,7 @@ func loadServerFrom(rootCfg ConfigProvider) {
+ 	OfflineMode = sec.Key("OFFLINE_MODE").MustBool()
+ 	Log.DisableRouterLog = sec.Key("DISABLE_ROUTER_LOG").MustBool()
+ 	if len(StaticRootPath) == 0 {
+-		StaticRootPath = AppWorkPath
++		StaticRootPath = "@data@"
+ 	}
+ 	StaticRootPath = sec.Key("STATIC_ROOT_PATH").MustString(StaticRootPath)
+ 	StaticCacheTime = sec.Key("STATIC_CACHE_TIME").MustDuration(6 * time.Hour)