Update ipython requirement from <=8.6.0 to <8.9.0 (#767)

Updates the requirements on [ipython](https://github.com/ipython/ipython) to permit the latest version.
- [Release notes](https://github.com/ipython/ipython/releases)
- [Commits](ipython/ipython@rel-0.8.4...8.8.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docs/notebook-requirements.txt

@@ -1,5 +1,5 @@
 # Jupyter notebooks
-ipython<=8.6.0
+ipython<8.9.0
 # ipython 8.7 introduced a bug regarding pygments lexer support
 # https://github.com/spatialaudio/nbsphinx/issues/24
 # https://github.com/ipython/ipython/issues/13845