fix(test): Fix flaky organization trace test sorting (#97831)

# Goal

The goal of this PR is to fix the flakiness reported in GH-97781. The
unit test `test_uptime_root_tree_with_orphaned_spans` in
`tests/snuba/api/endpoints/test_organization_trace.py` is randomly
failing in the CI with this error:

```
AssertionError: Span 0 differs (excluding children)
assert {'additional_...06400.15, ...} == {'additional_...906400.3, ...}
  
  Omitting 15 identical items, use -vv to show
  Differing items:
  {'duration': 150.0} != {'duration': 300.0}
  {'description': 'Uptime Check [success] - https://www.example.com/ (200)'} != {'description': 'Uptime Check [success] - https://example.com/ (301)'}
...
```

# Explanation of the flakiness

The failing assertion is:


https://github.com/getsentry/sentry/blob/3fa39f0740f17dab4c934b352525dbb5978e8f6e/tests/snuba/api/endpoints/test_organization_trace.py#L669-L673

`assert_expected_results` is a helper method defined in the test class
which asserts that the API response matches expected results from input
trace items. To do this, it sorts both the API response and the input
trace item with a `(guid, request_sequence)` custom sort key:


https://github.com/getsentry/sentry/blob/3fa39f0740f17dab4c934b352525dbb5978e8f6e/tests/snuba/api/endpoints/test_organization_trace.py#L465-L476

The issue is that the API response items don't have an `attributes` key
but only an `additional_attributes` key. In the `sort_key` method, their
`guid` will therefore default to their `event_id`, which is a
randomly-generated UUID. While input trace items (`[redirect_result,
final_result]`) will be ordered deterministically (based on their
`request_sequence`, since they have the same `guid` of `check-123`), API
response items will be ordered randomly based on their random UUID,
making the assertion fail randomly (because the assertion doesn't
compare related items).

You can easily reproduce the failure locally by running the test 10
times in a row:

```
for i in {1..10}; do pytest tests/snuba/api/endpoints/test_organization_trace.py::OrganizationEventsTraceEndpointTest::test_with_uptime_results ||
  exit 1; done
```

It should fail at least once.

# Fix

The fix is simple: rely on `additional_attributes["guid"]` to sort the
API response items. Incidentally, it's exactly what is done to get the
sequence number:


https://github.com/getsentry/sentry/blob/3fa39f0740f17dab4c934b352525dbb5978e8f6e/tests/snuba/api/endpoints/test_organization_trace.py#L471-L475

We just need to use the same syntax.

# Reproduction

Run the test 10 times in a row locally (same command as above) and see
that it now passes consistently.

# Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated
in the State of Delaware in 2015 as Functional Software, Inc. and is
gonna need some rights from me in order to utilize my contributions in
this here PR. So here's the deal: I retain all rights, title and
interest in and to my contributions, and by keeping this boilerplate
intact I confirm that Sentry can use, modify, copy, and redistribute my
contributions, under Sentry's choice of terms.

Author: floels

tests/snuba/api/endpoints/test_organization_trace.py

@@ -466,7 +466,7 @@ def sort_key(item):
             guid = (
                 item.attributes.get("guid", ProtoAttributeValue(val_str="")).string_value
                 if hasattr(item, "attributes")
-                else item.get("event_id", "")
+                else item.get("additional_attributes", {}).get("guid", "")
             )
             seq = (
                 item.attributes.get("request_sequence", ProtoAttributeValue(val_int=0)).int_value