Bump pybind11 from 2.7.1 to 2.8.1 in /dependencies (#2087)

Bumps [pybind11](https://github.com/pybind/pybind11) from 2.7.1 to 2.8.1.
- [Release notes](https://github.com/pybind/pybind11/releases)
- [Changelog](https://github.com/pybind/pybind11/blob/master/docs/changelog.rst)
- [Commits](https://github.com/pybind/pybind11/compare/v2.7.1...v2.8.1)

---
updated-dependencies:
- dependency-name: pybind11
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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dependencies/Pipfile.lock

@@ -837,11 +837,11 @@
         },
         "pybind11": {
             "hashes": [
-                "sha256:34663b2a16e7ac6ae8b77fef13e2b135e9fbc5ec13d2505d34bd35b3a41b9d82",
-                "sha256:8950aac5e5f4d505f7a0f067c5cb3893dcf098ff29cedfcb4ccf1e9e44d0bd9a"
+                "sha256:2ff4e50f171e3ae12b11c69e6ad49b05aa5e4b7eaa17b8148bee3cb3f0e4284b",
+                "sha256:4ecbc2a0d4d1f3636edd8296705cc164991b704f3389ebcfa52986a0101f913b"
             ],
             "index": "pypi",
-            "version": "==2.7.1"
+            "version": "==2.8.1"
         },
         "pycodestyle": {
             "hashes": [