tests: correct validation test-version entry

Corrects the used variable when populating a test version with the
source link configuration.

Signed-off-by: James Knight <james.d.knight@live.com>

tests/test_validation.py

@@ -58,7 +58,7 @@ def setUpClass(cls):
         cls.config['manpages_url'] = 'https://example.org/{path}'
         cls.test_desc = os.getenv(TESTDESC_ENV_KEY, DEFAULT_TEST_DESC)
         cls.test_key = os.getenv(TESTKEY_ENV_KEY, DEFAULT_TEST_KEY)
-        cls.test_version = os.getenv(TESTKEY_ENV_KEY, DEFAULT_TEST_VERSION)
+        cls.test_version = os.getenv(TESTKEY_ENV_VERSION, DEFAULT_TEST_VERSION)
 
         # overrides from user
         try: