fix: Workaround for Pandas Timestamp.isoformat issue

[john-bodley]

SUMMARY

The Pandas timestamp differs from the datetime.datetime object and the isoformat function doesn't include the timespec argument (the help description is wrong), i.e., it results in errors of the form,

TypeError: isoformat() got an unexpected keyword argument 'timespec

See pandas-dev/pandas#26131 for more details. The fix is to convert the pandas.TImestampobject into adatetime.datetime` object which is consistent with the existing logic, even though

>>> isinstance(pd.Timestamp('2021-11-12'), datetime.datetime)
True

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

CI and tested manually, i.e., checked the return type.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #17426 (8e5b0ea) into master (bcef8fa) will decrease coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #17426      +/-   ##
==========================================
- Coverage   76.96%   76.82%   -0.14%     
==========================================
  Files        1041     1041              
  Lines       56066    56066              
  Branches     7738     7738              
==========================================
- Hits        43150    43073      -77     
- Misses      12658    12735      +77     
  Partials      258      258              

Flag	Coverage Δ
hive	?
javascript	71.22% <ø> (ø)
mysql	81.93% <100.00%> (ø)
postgres	81.94% <100.00%> (ø)
python	82.03% <100.00%> (-0.27%)	⬇️
sqlite	81.62% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/utils/date_parser.py	96.63% <100.00%> (ø)
superset/db_engines/hive.py	0.00% <0.00%> (-85.19%)	⬇️
superset/db_engine_specs/hive.py	69.49% <0.00%> (-16.99%)	⬇️
superset/views/database/mixins.py	81.03% <0.00%> (-1.73%)	⬇️
superset/db_engine_specs/presto.py	83.47% <0.00%> (-0.84%)	⬇️
superset/db_engine_specs/base.py	88.20% <0.00%> (-0.39%)	⬇️
superset/connectors/sqla/models.py	86.35% <0.00%> (-0.24%)	⬇️
superset/utils/core.py	89.98% <0.00%> (-0.13%)	⬇️

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