Fix syntax error on Readme.rst (#20288)

### Description
<!-- Describe your changes. -->



### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
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docs/python/README.rst

@@ -6,18 +6,17 @@ For more information on ONNX Runtime, please see `aka.ms/onnxruntime <https://ak
 
 
 Changes
+-------
 
 1.17.3
 ^^^^^^
 
 Release Notes : https://github.com/Microsoft/onnxruntime/releases/tag/v1.17.3
--------
 
 1.17.2
 ^^^^^^
 
 Release Notes : https://github.com/Microsoft/onnxruntime/releases/tag/v1.17.2
--------
 
 1.17.1
 ^^^^^^