BUG: tz_localize(UTC) not making a copy

[jbrockmendel]

• closes #xxxx (Replace xxxx with the Github issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[jreback]

https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=75654&view=logs&j=915dbb23-6529-54ae-059d-ec0b59ba10e8&t=86b091c2-17fe-52fe-2454-5f56a371e155 looks legit

[jbrockmendel]

I think thats the test that #46450 fixed

[mroeschke]

Probably good to test with utc_fixture.

Also based on the code change None also returns a copy now too (and should be tested)?

[jbrockmendel]

sure. will use the fixture in the index tests and do the None just once in the tslibs tests

[mroeschke]

Warrants a whatsnew?

[mroeschke]

You may be aware, but looks like this PR didn't fully pass the CI checks

https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=75723&view=logs&jobId=f64eb602-b0ed-5dcc-0a60-a7288ad39597&j=f64eb602-b0ed-5dcc-0a60-a7288ad39597&t=129bd72d-2137-55bd-1811-c4ce50c6dce8

_______________________ test_tz_localize_to_utc_copies ________________________
[gw1] win32 -- Python 3.8.12 C:\Miniconda\envs\pandas-dev\python.exe

    def test_tz_localize_to_utc_copies():
        # GH#46460
        arr = np.arange(5, dtype="i8")
        result = tzconversion.tz_convert_from_utc(arr, tz=UTC)
        tm.assert_numpy_array_equal(result, arr)
        assert not np.shares_memory(arr, result)
    
>       result = tzconversion.tz_convert_from_utc(arr, tz=None)

pandas\tests\tslibs\test_conversion.py:60: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
pandas\_libs\tslibs\tzconversion.pyx:506: in pandas._libs.tslibs.tzconversion.tz_convert_from_utc
    converted = _tz_convert_from_utc(vals, tz)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

>   local_val = utc_val + deltas[pos]
E   UnboundLocalError: local variable 'deltas' referenced before assignment

pandas\_libs\tslibs\tzconversion.pyx:571: UnboundLocalError

[jbrockmendel]

yah, #46478 includes a fix

[jbrockmendel]

also #46489 is a targeted fix