add eval file async900_trio (#376)

Author: jakkdl

tests/eval_files/async900_trio.py

@@ -0,0 +1,15 @@
+import trio
+
+# different error message & no as_safe_channel
+# NOANYIO
+# NOASYNCIO
+
+
+async def foo1():  # ASYNC900: 0, 'trio.as_safe_channel, contextlib.asynccontextmanager, pytest.fixture'
+    yield
+    yield
+
+
+@trio.as_safe_channel
+async def foo():
+    yield