Bump src/deps/pybind11 from 8a099e4 to 31d7c87

Bumps [src/deps/pybind11](https://github.com/pybind/pybind11) from `8a099e4` to `31d7c87`.
- [Release notes](https://github.com/pybind/pybind11/releases)
- [Commits](pybind/pybind11@8a099e4...31d7c87)

---
updated-dependencies:
- dependency-name: src/deps/pybind11
  dependency-type: direct:production
...

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Author: dependabot[bot]