pip prod(deps): update ipympl requirement from <0.9.8 to <0.9.9

Updates the requirements on [ipympl](https://github.com/matplotlib/ipympl) to permit the latest version.
- [Release notes](https://github.com/matplotlib/ipympl/releases)
- [Changelog](https://github.com/matplotlib/ipympl/blob/main/RELEASE.md)
- [Commits](matplotlib/ipympl@0.0.1...v0.9.8)

---
updated-dependencies:
- dependency-name: ipympl
  dependency-version: 0.9.8
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements-testing.txt

@@ -7,4 +7,4 @@ scipy<1.15.4
 pooch<1.8.3
 click<9.0
 cloudpickle<3.1.2
-ipympl<0.9.8
+ipympl<0.9.9