Bump tensorflow in /tensorflow/lite/micro/examples/magic_wand/train

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 2.4.0 to 2.7.2.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v2.4.0...v2.7.2)

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

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Author: dependabot[bot]

tensorflow/lite/micro/examples/magic_wand/train/requirements.txt

@@ -1,2 +1,2 @@
 numpy==1.16.2
-tensorflow==2.5.0
+tensorflow==2.7.2