Change bus action += or __iadd__ behavior

[Tezirg]

Environment

• Grid2op version: 0.9.4
• System: Ubuntu20.04

Bug description

It seems using the += operator with change_bus action is not working correctly.
Bus changes are transformed into bus sets actions, with invalid bus index. (Here, bus 3 in the provided snippet)

How to reproduce

Command line

Code snippet

import grid2op

env = grid2op.make("rte_case14_realistic")
t =  env.action_space({})
t1 = env.action_space({
    "change_bus": {
        "substations_id": [(0, 0)]
    }
})
print (t)
print (t1)
t += t1
print (t)

Current output

This action will:
     - NOT change anything to the injections
     - NOT perform any redispatching action
     - NOT force any line status
     - NOT switch any line status
     - NOT switch anything in the topology
     - NOT force any particular bus configuration
This action will:
     - NOT change anything to the injections
     - NOT perform any redispatching action
     - NOT force any line status
     - NOT switch any line status
     - Change the bus of the following element:
          - switch bus of line (origin) 0 [on substation 0]
     - NOT force any particular bus configuration
This action will:
     - NOT change anything to the injections
     - NOT perform any redispatching action
     - NOT force any line status
     - NOT switch any line status
     - NOT switch anything in the topology
     - Set the bus of the following element:
          - assign bus 3 to line (origin) 0 [on substation 0]

Expected output

This action will:
     - NOT change anything to the injections
     - NOT perform any redispatching action
     - NOT force any line status
     - NOT switch any line status
     - NOT switch anything in the topology
     - NOT force any particular bus configuration
This action will:
     - NOT change anything to the injections
     - NOT perform any redispatching action
     - NOT force any line status
     - NOT switch any line status
     - Change the bus of the following element:
          - switch bus of line (origin) 0 [on substation 0]
     - NOT force any particular bus configuration
This action will:
     - NOT change anything to the injections
     - NOT perform any redispatching action
     - NOT force any line status
     - NOT switch any line status
     - Change the bus of the following element:
          - switch bus of line (origin) 0 [on substation 0]
     - NOT force any particular bus configuration

[BDonnot]

Issue addressed and fixed in 1.0.0