Bump dash in /examples/research_projects/decision_transformer

Bumps [dash](https://github.com/plotly/dash) from 2.3.0 to 2.15.0.
- [Release notes](https://github.com/plotly/dash/releases)
- [Changelog](https://github.com/plotly/dash/blob/dev/CHANGELOG.md)
- [Commits](plotly/dash@v2.3.0...v2.15.0)

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

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

examples/research_projects/decision_transformer/requirements.txt

@@ -38,7 +38,7 @@ cryptography==41.0.2
 csvw==2.0.0
 cycler==0.11.0
 Cython==0.29.28
-dash==2.3.0
+dash==2.15.0
 dash-bootstrap-components==1.0.3
 dash-core-components==2.0.0
 dash-html-components==2.0.0