BUG: ISO8601 fastpath fails to parse 2022-01-01 00:00:00Z

[MarcoGorelli]

Pandas version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

pd.to_datetime('2022-01-01 00:00:00Z', format='%Y-%m-%d %H:%M:%S%z')

Issue Description

Note how:

• in the standard library, %Z corresponds to 'UTC', not to 'Z'
• Z corresponds to '%z', not to '%Z'

In [6]: pydate = dt.datetime(2022, 11, 17, tzinfo=dt.timezone.utc)

In [7]: dt.datetime.strftime(pydate, '%Y-%m-%d %H:%M:%S%Z')
Out[7]: '2022-11-17 00:00:00UTC'

In [8]: dt.datetime.strptime('2020-01-01T00:00:00Z', '%Y-%m-%dT%H:%M:%S%z')
Out[8]: datetime.datetime(2020, 1, 1, 0, 0, tzinfo=datetime.timezone.utc)

Noticed while fixing merge conflicts in #49024 after having merged #49333

Expected Behavior

The ISO8601-fast-path should allow this string to be parsed with the given format

Installed Versions

INSTALLED VERSIONS

commit : 34b51d94d940f274652f60cf950b9cd2908ab7c3
python : 3.8.13.final.0
python-bits : 64
OS : Linux
OS-release : 5.10.102.1-microsoft-standard-WSL2
Version : #1 SMP Wed Mar 2 00:30:59 UTC 2022
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_GB.UTF-8
LOCALE : en_GB.UTF-8

pandas : 2.0.0.dev0+689.g34b51d94d9.dirty
numpy : 1.23.4
pytz : 2022.6
dateutil : 2.8.2
setuptools : 59.8.0
pip : 22.3.1
Cython : 0.29.32
pytest : 7.2.0
hypothesis : 6.56.4
sphinx : 4.5.0
blosc : None
feather : None
xlsxwriter : 3.0.3
lxml.etree : 4.9.1
html5lib : 1.1
pymysql : 1.0.2
psycopg2 : 2.9.3
jinja2 : 3.0.3
IPython : 8.6.0
pandas_datareader: 0.10.0
bs4 : 4.11.1
bottleneck : 1.3.5
brotli :
fastparquet : 0.8.3
fsspec : 2021.11.0
gcsfs : 2021.11.0
matplotlib : 3.6.2
numba : 0.56.3
numexpr : 2.8.3
odfpy : None
openpyxl : 3.0.10
pandas_gbq : 0.17.9
pyarrow : 9.0.0
pyreadstat : 1.2.0
pyxlsb : 1.0.10
s3fs : 2021.11.0
scipy : 1.9.3
snappy :
sqlalchemy : 1.4.43
tables : 3.7.0
tabulate : 0.9.0
xarray : 2022.11.0
xlrd : 2.0.1
zstandard : 0.19.0
tzdata : None
qtpy : None
pyqt5 : None
None

[MarcoGorelli]

Looks like '%Z' was added to the format_is_iso function in https://github.com/pandas-dev/pandas/pull/42068/files

EDIT: this is a separate issue, will open one now