listers: Ensure run can be called without bounds arguments

Closes T2001

swh/lister/github/lister.py

@@ -16,6 +16,7 @@ class GitHubLister(IndexingHttpLister):
     API_URL_INDEX_RE = re.compile(r'^.*/repositories\?since=(\d+)')
     LISTER_NAME = 'github'
     instance = 'github'  # There is only 1 instance of such lister
+    default_min_bound = 0
 
     def get_model_from_repo(self, repo):
         return {

swh/lister/github/tests/test_gh_lister.py

@@ -16,7 +16,7 @@ class GitHubListerTester(HttpListerTester, unittest.TestCase):
     lister_subdir = 'github'
     good_api_response_file = 'api_response.json'
     bad_api_response_file = 'api_empty_response.json'
-    first_index = 26
+    first_index = 0
     last_index = 368
     entries_per_page = 100
     convert_type = int