tests/micropython: Add a test for throwing incomplete exception.

This is a reproducer for #17117.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>

tests/micropython/incomplete_exc.py

@@ -0,0 +1,40 @@
+# Test raising an incomplete exception.
+
+
+class C(Exception):
+    def __init__(self):
+        raise self
+
+
+class C1(C):
+    pass
+
+
+class B:
+    pass
+
+
+class C2(B, Exception):
+    def __init__(self):
+        raise self
+
+
+class C3(Exception, B):
+    def __init__(self):
+        raise self
+
+
+class D(Exception):
+    pass
+
+
+class C4(D):
+    def __init__(self):
+        raise self
+
+
+for cls in C, C1, C2, C3, C4:
+    try:
+        cls()
+    except TypeError as e:
+        print("TypeError")

tests/micropython/incomplete_exc.py.exp

@@ -0,0 +1,5 @@
+TypeError
+TypeError
+TypeError
+TypeError
+TypeError