ci/docs: build documentation for the nixos-25.05 branch

Author: GaetanLepage

.github/workflows/build_documentation.yml

@@ -57,6 +57,11 @@ jobs:
                 "branch": "main",
                 "nixpkgsBranch": "nixos-unstable"
               },
+              {
+                "branch": "nixos-25.05",
+                "nixpkgsBranch": "nixos-25.05",
+                "subPath": "25.05"
+              },
               {
                 "branch": "nixos-24.11",
                 "nixpkgsBranch": "nixos-24.11",