Handle missing ukpostcodeparser gracefully in tests (joke2k#1383)

Skip the single test relying on ukpostcodeparser if the relevant package
is not installed on the system.  There are users who don't really need
that particular function and appreciate the ability to test Faker
before installing it on their production systems.

tests/providers/test_address.py

@@ -4,8 +4,6 @@
 
 import pytest
 
-from ukpostcodeparser.parser import parse_uk_postcode
-
 from faker.providers.address.cs_CZ import Provider as CsCzAddressProvider
 from faker.providers.address.da_DK import Provider as DaDkAddressProvider
 from faker.providers.address.de_AT import Provider as DeAtAddressProvider
@@ -381,8 +379,9 @@ class TestEnGb:
     """Test en_GB address provider methods"""
 
     def test_postcode(self, faker, num_samples):
+        ukpcp = pytest.importorskip('ukpostcodeparser.parser')
         for _ in range(num_samples):
-            assert isinstance(parse_uk_postcode(faker.postcode()), tuple)
+            assert isinstance(ukpcp.parse_uk_postcode(faker.postcode()), tuple)
 
     def test_county(self, faker, num_samples):
         for _ in range(num_samples):