chore(deps): update ipykernel requirement from ==6.25.* to ==6.26.*

Updates the requirements on [ipykernel](https://github.com/ipython/ipykernel) to permit the latest version.
- [Release notes](https://github.com/ipython/ipykernel/releases)
- [Changelog](https://github.com/ipython/ipykernel/blob/main/CHANGELOG.md)
- [Commits](ipython/ipykernel@v6.25.0...v6.26.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

requirements-research.txt

@@ -1,3 +1,3 @@
-ipykernel==6.25.*
+ipykernel==6.26.*
 matplotlib==3.8.*
 pandas==2.1.*