tests: Add test for modure when regex has errors.

tests/extmod/ure_error.py

@@ -0,0 +1,21 @@
+# test errors in regex
+
+try:
+    import ure as re
+except:
+    import re
+
+def test_re(r):
+    try:
+        re.compile(r)
+        print("OK")
+    except: # uPy and CPy use different errors, so just ignore the type
+        print("Error")
+
+test_re(r'?')
+test_re(r'*')
+test_re(r'+')
+test_re(r')')
+test_re(r'[')
+test_re(r'([')
+test_re(r'([)')