Update sphinx-copybutton requirement from ~=0.5.0 to ~=0.5.1 (#129)

Updates the requirements on [sphinx-copybutton](https://github.com/executablebooks/sphinx-copybutton) to permit the latest version.
- [Release notes](https://github.com/executablebooks/sphinx-copybutton/releases)
- [Changelog](https://github.com/executablebooks/sphinx-copybutton/blob/master/CHANGELOG.md)
- [Commits](executablebooks/sphinx-copybutton@v0.5.0...v0.5.1)

---
updated-dependencies:
- dependency-name: sphinx-copybutton
  dependency-type: direct:production
...

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Author: dependabot[bot]

requirements-docs.txt

@@ -12,5 +12,5 @@
 ipython ~=7.34.0
 numpydoc ~=1.5
 sphinx ~=5.3.0
-sphinx-copybutton ~=0.5.0
+sphinx-copybutton ~=0.5.1
 sphinx_rtd_theme ~=1.0.0