stalwart-mail: patch service file to fix module compat

We're using the upstream systemd service file since dfa130e.
It specifies `PermissionsStartOnly = true`, which is not only
deprecated in recent systemd, but also interferes with the
`ExecPreStart` in our module.

This adds a patch to the package solving this, allowing our module and
NixOS test to work until this gets merged upstream.

Upstream PR: https://github.com/stalwartlabs/mail-server/pull/528

pkgs/by-name/st/stalwart-mail/package.nix

@@ -1,6 +1,7 @@
 { lib
 , rustPlatform
 , fetchFromGitHub
+, fetchpatch
 , pkg-config
 , protobuf
 , bzip2
@@ -38,6 +39,16 @@ rustPlatform.buildRustPackage {
 
   cargoHash = "sha256-w40mksUVMBXSr/LBXj0uyZ/VbvJFMFJaQN5Kx6sLm5I=";
 
+  patches = [
+    # Remove "PermissionsStartOnly" from systemd service files,
+    # which is deprecated and conflicts with our module's ExecPreStart.
+    # Upstream PR: https://github.com/stalwartlabs/mail-server/pull/528
+    (fetchpatch {
+      url = "https://github.com/stalwartlabs/mail-server/pull/528/commits/6e292b3d7994441e58e367b87967c9a277bce490.patch";
+      hash = "sha256-j/Li4bYNE7IppxG3FGfljra70/rHyhRvDgOkZOlhMHY=";
+    })
+  ];
+
   nativeBuildInputs = [
     pkg-config
     protobuf