fix: retry a bad data download, keep the site step

The buildbot answered once with something that was not ScummVM.zip. refresh_data_dirs gave up at once, Generate the site was skipped, and 228 site tests failed in its place. A failed or unreadable download is now tried three times, with waits of 5 and 20 s, and an empty archive still fails at once. The site step runs after a failed fetch, which stays red on its own step.

tests/test_workflow_paths.py

@@ -143,6 +143,9 @@ class ThePullRequestBuildsTheSite(unittest.TestCase):
         suite = next(i for i, run in enumerate(runs) if "unittest discover" in run)
         self.assertLess(generate, suite)
         self.assertEqual(steps[suite].get("if"), "${{ !cancelled() }}")
+        # A failed data fetch skipped the generator, and all 228 site tests
+        # then failed under it: the generator runs whatever came before.
+        self.assertEqual(steps[generate].get("if"), "${{ !cancelled() }}")
 
     def test_every_site_input_triggers_validation(self):
         deploy = self._workflow("deploy-site.yml")