tz_compare fails to consider string "UTC" and pytz UTC object equal
Nothing user-facing here, but this surprised me.

```python
In [5]: pd._libs.tslibs.timezones.tz_compare("UTC", pytz.timezone("UTC"))
Out[5]: False
```

Other timezones behave as expected

```
In [6]: pd._libs.tslibs.timezones.tz_compare("US/Eastern", pytz.timezone("US/Eastern"))
Out[6]: True
```

Is this user error, or a bug?