chore: bump gunicorn to 20.1.0

[mporracindie]

SUMMARY

Bumping gunicorn to 20.1.0 due to security vulnerability.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

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 #17894 (6274068) into master (8ebec60) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #17894      +/-   ##
==========================================
- Coverage   67.10%   67.09%   -0.01%     
==========================================
  Files        1609     1609              
  Lines       64897    64897              
  Branches     6866     6866              
==========================================
- Hits        43547    43545       -2     
- Misses      19484    19486       +2     
  Partials     1866     1866              

Flag	Coverage Δ
hive	81.81% <ø> (ø)
mysql	82.19% <ø> (ø)
postgres	82.24% <ø> (ø)
presto	82.10% <ø> (-0.01%)	⬇️
python	82.72% <ø> (-0.01%)	⬇️
sqlite	81.92% <ø> (ø)

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

Impacted Files	Coverage Δ
superset/db_engine_specs/presto.py	89.97% <0.00%> (-0.42%)	⬇️

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