Fix #1292 files_upload_v2 does not work with io.BytesIO file parameters

[seratch]

Summary

This pull request resolves #1292

Category (place an x in each of the [ ])

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.signature (Request Signature Verifier)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.models (UI component builders)
• slack_sdk.scim (SCIM API client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.rtm_v2 (RTM client)
• /docs-src (Documents, have you run ./scripts/docs.sh?)
• /docs-src-v2 (Documents, have you run ./scripts/docs-v2.sh?)
• /tutorial (PythOnBoardingBot tutorial)
• tests/integration_tests (Automated tests for this library)

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes.

[codecov]

Codecov Report

Merging #1294 (ef62d6c) into main (db17415) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1294      +/-   ##
==========================================
+ Coverage   85.62%   85.63%   +0.01%     
==========================================
  Files          84       84              
  Lines        7827     7827              
==========================================
+ Hits         6702     6703       +1     
+ Misses       1125     1124       -1     

Impacted Files	Coverage Δ
slack_sdk/socket_mode/builtin/internals.py	72.53% <0.00%> (+0.42%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[WilliamBergamin]

This looks good to me, thanks for getting to this 💯

[seratch]

Thanks for the review!