update our updating instructions

### Proposed documentation enhancement

Since version 4.14.0 (2022 August), [`conda rename` is possible](https://docs.conda.io/projects/conda/en/latest/release-notes.html#id30).  Our docs say otherwise: 

https://github.com/mne-tools/mne-python/blob/468aae3daf975c0a81bf3a33a2037e078920bde6/doc/install/updating.rst?plain=1#L45

we should correct them.