[cherry-pick]increase test_imperative_auto_mixed_precision time PROPERTIES...

 [cherry-pick]increase test_imperative_auto_mixed_precision time PROPERTIES TIMEOUT (#35863) (#35898)

Increase test_imperative_auto_mixed_precision PROPERTIES TIMEOUT from 120s to 300s.

python/paddle/fluid/tests/unittests/CMakeLists.txt

@@ -1029,7 +1029,7 @@ if((WITH_ROCM OR WITH_GPU) AND NOT WIN32)
     set_tests_properties(test_collective_sendrecv PROPERTIES TIMEOUT 120)
 endif()
 if(WITH_GPU OR WITH_ROCM)
-    set_tests_properties(test_imperative_auto_mixed_precision PROPERTIES TIMEOUT 120)
+    set_tests_properties(test_imperative_auto_mixed_precision PROPERTIES TIMEOUT 300)
     set_tests_properties(test_parallel_dygraph_sync_batch_norm PROPERTIES TIMEOUT 120)
     set_tests_properties(test_rank_attention_op PROPERTIES TIMEOUT 120)
 endif()