Catch `ChannelInvalidStateError` in process state change

[sphuber]

In Process.on_entered, the Communicator.broadcast_send method is called to broadcast the state change to subscribers over RabbitMQ. This can throw a ChannelInvalidStateError in addition to the ConnectionClose exception that was already being caught, in case there is a problem with the connection.

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (98a375f) 90.72% compared to head (a7b75f1) 90.72%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## support/0.21.x #278 +/- ## =============================================== Coverage 90.72% 90.72% =============================================== Files 22 22 Lines 2995 2995 =============================================== Hits 2717 2717 Misses 278 278 ``` | [Files](https://app.codecov.io/gh/aiidateam/plumpy/pull/278?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidateam) | Coverage Δ | | |---|---|---| | [src/plumpy/processes.py](https://app.codecov.io/gh/aiidateam/plumpy/pull/278?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aiidateam#diff-c3JjL3BsdW1weS9wcm9jZXNzZXMucHk=) | `92.47% <50.00%> (ø)` | |

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