IPv6 addresses are not allowed to start with a single leading ':'

Fix failing tests.

Author: EdwardBetts

tests/test_util.py

@@ -17,9 +17,9 @@
 def test_normalize_url():
     assert normalize_url("http://1.2.3.4:80") == "http://1.2.3.4:80"
     assert normalize_url("http://1.2.3.4:80:80") == "http://1.2.3.4:80"
-    assert normalize_url("http://[:dead:beef::1]:80") == "http://[:dead:beef::1]:80"
+    assert normalize_url("http://[dead:beef::1]:80") == "http://[dead:beef::1]:80"
     assert normalize_url(None) is None
-    assert normalize_url(b"http://[:dead:beef::1]:80") is None
+    assert normalize_url(b"http://[dead:beef::1]:80") is None
 
 
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