Flappy Elixir test

[tsloughter]

This test often needs to be rerun in CI before it passes:

  1) test use explicit Context for parent of started Span (OtelTests)
Error:      test/otel_tests.exs:182
     Assertion failed, no matching message after 100ms
     The following variables were pinned:
       attributes = {:attributes, 128, :infinity, 0, %{"attr-1" => "value-1", "attr-2" => "value-2"}}
     The process mailbox is empty.
     code: assert_receive {:span, span(name: "span-1", parent_span_id: :undefined, attributes: ^attributes)}
     stacktrace:
       test/otel_tests.exs:203: (test)