[AMD] Add TP=8 models to nightly test and make TP=2 test stable (#15296)

test/srt/run_suite.py

@@ -317,6 +317,10 @@ suite_amd = {
     "nightly-amd": [
         TestFile("nightly/test_gsm8k_eval_amd.py"),
     ],
+    # AMD 8-GPU tests for base models using gsm8k completion benchmark
+    "nightly-amd-8-gpu": [
+        TestFile("nightly/test_gsm8k_completion_eval_amd.py"),
+    ],
 }
 
 # Add Intel Xeon tests