Bump mxnet from 1.6.0 to 1.9.1

Bumps [mxnet](https://github.com/apache/incubator-mxnet) from 1.6.0 to 1.9.1.
- [Release notes](https://github.com/apache/incubator-mxnet/releases)
- [Changelog](https://github.com/apache/incubator-mxnet/blob/master/NEWS.md)
- [Commits](apache/mxnet@1.6.0...1.9.1)

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

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

pyproject.toml

@@ -9,7 +9,7 @@ python = ">=3.8.0,<3.9.7 || >3.9.7,<3.11"
 atoti = {extras = ["jupyterlab", "kafka", "aws", "azure", "gcp"], version = "^0.7.0"}
 wget = "^3.2"
 treelib = "^1.6.1"
-mxnet = "1.6.0"
+mxnet = "1.9.1"
 matplotlib = "^3.4.2"
 gluonts = "^0.7.5"
 folium = "^0.12.1"