Update tests/test_additional_headers_simple.py

Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

Author: hassiebp

tests/test_additional_headers_simple.py

@@ -180,4 +180,4 @@ def test_span_processor_none_additional_headers_works(self):
         # Verify default headers are present
         assert "Authorization" in exporter._headers
         assert "x-langfuse-sdk-name" in exporter._headers
-        assert "x_langfuse_public_key" in exporter._headers
+        assert "x-langfuse-public-key" in exporter._headers