fix: change type of slack error

[eschutho]

SUMMARY

Small change to log a 400 error if there are slack api errors caught. Also fixes a parsing error in the exception handling where we were trying to parse an exception as a string.

TESTING INSTRUCTIONS

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 #22443 (248160a) into master (605cfa0) will decrease coverage by 11.30%.
The diff coverage is 58.15%.

❗ Current head 248160a differs from pull request most recent head 4831a83. Consider uploading reports for the commit 4831a83 to get more accurate results

@@             Coverage Diff             @@
##           master   #22443       +/-   ##
===========================================
- Coverage   66.86%   55.56%   -11.31%     
===========================================
  Files        1847     1850        +3     
  Lines       70574    70699      +125     
  Branches     7748     7750        +2     
===========================================
- Hits        47190    39283     -7907     
- Misses      21383    29400     +8017     
- Partials     2001     2016       +15     

Flag	Coverage Δ
hive	?
mysql	?
postgres	?
presto	52.36% <33.18%> (-0.07%)	⬇️
python	57.43% <61.36%> (-23.80%)	⬇️
sqlite	?
unit	50.95% <59.54%> (+0.03%)	⬆️

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

Impacted Files	Coverage Δ
...ars/src/components/ControlHeader/controlHeader.tsx	50.00% <ø> (ø)
...ars/src/components/Handlebars/HandlebarsViewer.tsx	0.00% <0.00%> (ø)
...gin-chart-handlebars/src/plugin/controls/style.tsx	28.57% <0.00%> (ø)
...ugin-chart-table/src/DataTable/hooks/useSticky.tsx	53.26% <ø> (+1.68%)	⬆️
...rontend/src/views/CRUD/dashboard/DashboardList.tsx	56.60% <ø> (ø)
superset/databases/api.py	52.30% <ø> (-41.24%)	⬇️
superset/db_engine_specs/hive.py	34.25% <0.00%> (-53.10%)	⬇️
superset/reports/commands/exceptions.py	89.34% <ø> (-9.05%)	⬇️
superset/reports/notifications/slack.py	33.33% <0.00%> (-46.19%)	⬇️
superset/reports/types.py	100.00% <ø> (ø)
... and 313 more

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[sadpandajoe]

🏷️ preset:2023.01