chore: bump gym from 0.21.0 to 0.26.0

Bumps [gym](https://github.com/openai/gym) from 0.21.0 to 0.26.0.
- [Release notes](https://github.com/openai/gym/releases)
- [Commits](openai/gym@v0.21.0...0.26.0)

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

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

Author: dependabot[bot]

poetry.lock

@@ -12,7 +12,7 @@ documentation = "https://eagerx.readthedocs.io/en/master/"
 python = "^3.6.2"
 opencv-python = "^4.3.0.36"
 networkx = "^2.5.1"
-gym = "^0.21.0"
+gym = ">=0.21,<0.27"
 tabulate = "^0.8.9"
 PyYAML = "^6.0"
 rospkg = "^1.3.0"