Bump pip from 23.1.2 to 23.3 in /backend (#293)

Bumps [pip](https://github.com/pypa/pip) from 23.1.2 to 23.3.
- [Changelog](https://github.com/pypa/pip/blob/main/NEWS.rst)
- [Commits](pypa/pip@23.1.2...23.3)

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

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backend/requirements.txt

@@ -1,4 +1,4 @@
-pip==23.1.2
+pip==23.3
 setuptools==68.0.0
 wheel==0.40.0
 neurolink