[rocm7.0_internal_testing] skip test_all_gather_extensions_train_parity if world_size less then 2 (#2265)

Base class forces to use `world_size=2` even for 1 GPU. Then NCCL fails
with errors:
```
ncclInvalidUsage: This usually reflects invalid usage of NCCL library.
Duplicate GPU detected : rank 1 and rank 0 both on CUDA device c000
Duplicate GPU detected : rank 0 and rank 1 both on CUDA device c000
```
This PR will skip FSDP tests if `world_size > torch.cuda.device_count()`
```
HIP_VISIBLE_DEVICES=0 pytest -v distributed/_composable/fsdp/test_fully_shard_extensions.py::TestFullyShardAllGatherExtensionsMultiProcess::test_all_gather_extensions_train_parity

dist init r=0, world=2
dist init r=1, world=2
SKIPPED [15.5507s] (Need at least 2 CUDA devices)
```
Fixes SWDEV-535767

Author: dnikolaev-amd

torch/testing/_internal/common_fsdp.py

@@ -1187,6 +1187,8 @@ def _run(cls, rank, test_name, file_name, pipe, **kwargs):
         fake_pg = kwargs.get("fake_pg", False)
 
         print(f"dist init r={self.rank}, world={self.world_size}")
+        if torch.cuda.device_count() < self.world_size:
+            sys.exit(TEST_SKIPS[f"multi-gpu-{self.world_size}"].exit_code)
 
         # Specify gloo backend to make 'init_process_group()' succeed,
         # Actual tests will be skipped if there is no enough GPUs.