Fix replica groups issue 3676 (#3687)

* Complete Fix Replica Groups error

* Remove replica-list top-level resources validation; instead add comment

---------

Co-authored-by: Bihan  Rana

Author: Bihan

src/dstack/_internal/server/services/runs/spec.py

@@ -5,7 +5,6 @@
     ServiceConfiguration,
 )
 from dstack._internal.core.models.repos.virtual import DEFAULT_VIRTUAL_REPO_ID, VirtualRunRepoData
-from dstack._internal.core.models.resources import ResourcesSpec
 from dstack._internal.core.models.runs import LEGACY_REPO_DIR, AnyRunConfiguration, RunSpec
 from dstack._internal.core.models.volumes import InstanceMountPoint
 from dstack._internal.core.services import validate_dstack_resource_name
@@ -113,18 +112,10 @@ def validate_run_spec_and_set_defaults(
             raise ServerClientError(
                 f"Probe timeout cannot be longer than {settings.MAX_PROBE_TIMEOUT}s"
             )
-        if isinstance(run_spec.configuration.replicas, list):
-            default_resources = ResourcesSpec()
-            if (
-                run_spec.configuration.resources
-                and run_spec.configuration.resources.dict() != default_resources.dict()
-            ):
-                raise ServerClientError(
-                    "Top-level `resources` is not allowed when `replicas` is a list. "
-                    "Specify `resources` in each replica group instead."
-                )
     if run_spec.configuration.priority is None:
         run_spec.configuration.priority = RUN_PRIORITY_DEFAULT
+    # We do not reject top-level `resources` when `replicas` is a list. Adding strict checks
+    # would be fragile because the spec may be changed later (for example by plugins).
     set_resources_defaults(run_spec.configuration.resources)
     set_gpu_vendor_default(
         run_spec.configuration.resources,