BUG: DataFrame.plot(kind='scatter') does not raise KeyError when unknown colormap is applied

[lisphilar]

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

import pandas as pd
iris = pd.read_csv('https://raw.githubusercontent.com/mwaskom/seaborn-data/master/iris.csv')
iris.plot(x='sepal_length', y='sepal_width', colormap='unknown')
# -> TypeError raised as expected
iris.plot(x='sepal_length', y='sepal_width', colormap='unknown', kind='scatter')
# -> TypeError is expected but not raised at version 1.5.0

Issue Description

.plot(..., colormap='unknown') raises TypeError because the colormap is unknown, but .plot(..., colormap='unknown', kind='scatter') does raise TypeError.

Expected Behavior

.plot(..., cmap='unknown', kind='scatter') will raise TypeError.

Installed Versions

INSTALLED VERSIONS

commit : 87cfe4e
python : 3.10.7.final.0
python-bits : 64
OS : Linux
OS-release : 5.10.16.3-microsoft-standard-WSL2
Version : #1 SMP Fri Apr 2 22:23:49 UTC 2021
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : C.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.5.0
numpy : 1.23.3
pytz : 2022.2.1
dateutil : 2.8.2
setuptools : 65.3.0
pip : 22.2.2
Cython : None
pytest : 7.1.3
hypothesis : None
sphinx : 5.1.1
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.9.1
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.5.0
pandas_datareader: None
bs4 : 4.11.1
bottleneck : None
brotli : None
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : 3.6.0
numba : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 9.0.0
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.8.1
snappy : None
sqlalchemy : 1.4.41
tables : None
tabulate : 0.8.10
xarray : None
xlrd : None
xlwt : None
zstandard : None
tzdata : None

[phofl]

This will raise a Waring with the newest matplotlib, since colormap has no effect in that scenario, even if a valid value is passed

[lisphilar]

Thank you for your information and pull request!