tests: Add test for exception-chaining raise syntax.

tests/basics/exception_chain.py

@@ -0,0 +1,6 @@
+# Exception chaining is not supported, but check that basic
+# exception works as expected.
+try:
+    raise Exception from None
+except Exception:
+    print("Caught Exception")

tests/basics/exception_chain.py.exp

@@ -0,0 +1,2 @@
+Caught Exception
+Warning: exception chaining not supported