Add EHOSTUNREACH ('No route to host') to the errnos trapped by transient_internet().

Lib/test/support.py

@@ -800,6 +800,7 @@ def transient_internet(resource_name, *, timeout=30.0, errnos=()):
     default_errnos = [
         ('ECONNREFUSED', 111),
         ('ECONNRESET', 104),
+        ('EHOSTUNREACH', 113),
         ('ENETUNREACH', 101),
         ('ETIMEDOUT', 110),
     ]