fix(ssh-tunnel): wrap pkey into StringIO buffer before creating the tunnel

[hughhhh]

SUMMARY

Adding StringIO to wrap value before creating the tunnel to allow the pkg to properly read the private key needed to create the tunnel.

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 #22763 (2fd3c11) into master (c58dbf8) will decrease coverage by 11.31%.
The diff coverage is 40.00%.

❗ Current head 2fd3c11 differs from pull request most recent head 0966107. Consider uploading reports for the commit 0966107 to get more accurate results

@@             Coverage Diff             @@
##           master   #22763       +/-   ##
===========================================
- Coverage   67.23%   55.92%   -11.31%     
===========================================
  Files        1876     1876               
  Lines       71814    71818        +4     
  Branches     7863     7863               
===========================================
- Hits        48284    40165     -8119     
- Misses      21504    29627     +8123     
  Partials     2026     2026               

Flag	Coverage Δ
hive	52.59% <40.00%> (-0.01%)	⬇️
postgres	?
presto	52.49% <40.00%> (-0.01%)	⬇️
python	58.29% <40.00%> (-23.56%)	⬇️
sqlite	?
unit	51.53% <40.00%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
superset/extensions/ssh.py	64.10% <40.00%> (-1.62%)	⬇️
superset/utils/dashboard_import_export.py	0.00% <0.00%> (-100.00%)	⬇️
superset/tags/core.py	4.54% <0.00%> (-95.46%)	⬇️
superset/key_value/commands/update.py	0.00% <0.00%> (-90.91%)	⬇️
superset/key_value/commands/delete.py	0.00% <0.00%> (-87.88%)	⬇️
superset/key_value/commands/delete_expired.py	0.00% <0.00%> (-84.00%)	⬇️
superset/dashboards/commands/importers/v0.py	15.62% <0.00%> (-76.25%)	⬇️
superset/datasets/commands/create.py	30.61% <0.00%> (-69.39%)	⬇️
superset/datasets/commands/update.py	25.00% <0.00%> (-69.05%)	⬇️
superset/datasets/commands/importers/v0.py	24.03% <0.00%> (-69.00%)	⬇️
... and 293 more

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