Update to the latest source_span

R=jakemac@google.com

Change-Id: I88e2752ed453692cba6aae58699cc8154951ba71
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/240361
Auto-Submit: Nate Bosch <nbosch@google.com>
Reviewed-by: Jake Macdonald <jakemac@google.com>
Commit-Queue: Jake Macdonald <jakemac@google.com>

Author: natebosch

DEPS

@@ -153,7 +153,7 @@ vars = {
   "source_map_stack_trace_rev": "8eabd96b1811e30a11d3c54c9b4afae4fb72e98f",
   "source_maps-0.9.4_rev": "38524",
   "source_maps_rev": "6499ee3adac8d469e2953e2e8ba4bdb4c2fbef90",
-  "source_span_rev": "dc189b455d823e2919667f6c5dcb41ab7483bce0",
+  "source_span_rev": "8ae724c3e67f5afaacead44e93ff145bfb8775c7",
   "sse_rev": "9084339389eb441d0c0518cddac211a097e78657",
   "stack_trace_rev": "5220580872625ddee41e9ca9a5f3364789b2f0f6",
   "stream_channel_rev": "3fa3e40c75c210d617b8b943b9b8f580e9866a89",