Fix Gym repo version to the previous release.
0.26.0 includes backward-incompatible changes to Env.step interface.
@@ -80,7 +80,7 @@ envs_requirements = [
'atari-py',
'bsuite',
'dm-control==0.0.364896371', # TODO(b/206925413): update to new version.
- 'gym',
+ 'gym==0.25.0',
'gym[atari]',
'pygame==2.1.0',
'tensorflow-datasets==4.5.2',
