Allow using datetime64[ns, UTC] in IntervalDtype
The current regexp doesn't allow the use of comma in the interval `subtype`, which means this statement fails
```
pd.IntervalIndex.from_arrays([1, 2], [2, 3], dtype='interval[datetime64[ns, UTC], right]')
```
with `TypeError: data type 'interval[datetime64[ns, UTC], right]' not understood`

The proposed change allows the use of comma inside square brackets in the `subtype`.

Hello @helgehatt! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2022-04-06 13:37:04 UTC Thanks @helgehatt for the PR.

> The current regexp doesn't allow the use of comma in the interval `subtype`, which means this statement fails

If there is no existing issue for this, can you open one.
 This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. > Thanks @helgehatt for the PR.
> 
> > The current regexp doesn't allow the use of comma in the interval `subtype`, which means this statement fails
> 
> If there is no existing issue for this, can you open one.

opened #46999

closing this as stale.