Fix a transiently failing API test.

``` 'populated_state_message': 'Failed to fetch collection element(s):\n\n- Failed to fetch url https://raw.githubusercontent.com/galaxyproject/galaxy/dev/test-data/4.bed. HTTP Error 429: Too Many Requests',```

I've stopped writing tests like this since the base64 URIs were implemented, not depending on an external service - even one as dependable as Github - provides greater test isolation and robustness and walks essentially all the same code paths in terms of Galaxy code we'd like to test.

Author: jmchilton

lib/galaxy_test/api/test_dataset_collections.py

@@ -437,13 +437,13 @@ def test_upload_nested(self):
             element0 = hdca["elements"][0]
             assert element0["element_identifier"] == "samp1"
 
-    @skip_if_github_down
     def test_upload_collection_from_url(self):
         with self.dataset_populator.test_history(require_new=False) as history_id:
             elements = [
                 {
                     "src": "url",
-                    "url": "https://raw.githubusercontent.com/galaxyproject/galaxy/dev/test-data/4.bed",
+                    "url": self.dataset_populator.base64_url_for_string("hello world"),
+                    "name": "hello.txt",
                     "info": "my cool bed",
                 }
             ]
@@ -462,8 +462,8 @@ def test_upload_collection_from_url(self):
             hdca = self._assert_one_collection_created_in_history(history_id)
             assert len(hdca["elements"]) == 1, hdca
             element0 = hdca["elements"][0]
-            assert element0["element_identifier"] == "4.bed"
-            assert element0["object"]["file_size"] == 61
+            assert element0["element_identifier"] == "hello.txt"
+            assert element0["object"]["file_size"] == 11
 
     def test_upload_collection_deferred(self):
         with self.dataset_populator.test_history(require_new=False) as history_id: