Update tensorflow requirement in /src/bindings/python

Updates the requirements on [tensorflow](https://github.com/tensorflow/tensorflow) to permit the latest version.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v1.15.5...v2.20.0)

---
updated-dependencies:
- dependency-name: tensorflow
  dependency-version: 2.20.0
  dependency-type: direct:production
...

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Author: dependabot[bot]

src/bindings/python/constraints.txt

@@ -20,6 +20,6 @@ packaging>=22.0
 h5py>=3.1.0,<3.14.0
 docopt~=0.6.2
 paddlepaddle==2.6.2
-tensorflow>=1.15.5,<2.20.0
+tensorflow>=1.15.5,<2.21.0
 protobuf>=3.18.1,<7.0.0
 onnx==1.17.0