Fix all datetime calls that assume UTC timezone
The builtin python datetime module has historically included methods to force UTC datetimes. In someone's infinite wisdom, python has chosen to deprecate these, and instead force users to specify a datetime.UTC time zone (the deprecation warning for this is causing thousands of "warnings" to be issued in our unit tests presently.
Examples of solutions are:
```diff
import datetime as dt
# get the current UTC time from system clock
- utc_dt = dt.datetime.utcnow()
+ utc_dt = dt.datetime.now(dt.timezone.utc)
# get UTC time from timestamp
timestamp = dt.datetime(2022, 2, 22, 22, 22, 22).timestamp()
- utc_dt = dt.datetime.utcfromtimestamp(timestamp)
+ utc_dt = dt.datetime.fromtimestamp(timestamp, dt.timezone.utc)
```
(these examples are not exhaustive)
issue