tests/extmod: Add test for ure regexes leading to infinite recursion.

These now should be caught properly and lead to RuntimeError instead of
crash.

tests/extmod/ure_stack_overflow.py

@@ -0,0 +1,13 @@
+try:
+    import ure as re
+except ImportError:
+    try:
+        import re
+    except ImportError:
+        print("SKIP")
+        raise SystemExit
+
+try:
+    re.match("(a*)*", "aaa")
+except RuntimeError:
+    print("RuntimeError")

tests/extmod/ure_stack_overflow.py.exp

@@ -0,0 +1 @@
+RuntimeError