Fix #1236 Add video block to Block Kit model classes

[seratch]

Summary

This pull request resolves #1236

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 #1237 (dd2db0e) into main (5d509e0) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1237      +/-   ##
==========================================
+ Coverage   86.56%   86.60%   +0.03%     
==========================================
  Files         111      111              
  Lines       10986    11026      +40     
==========================================
+ Hits         9510     9549      +39     
- Misses       1476     1477       +1     

Impacted Files	Coverage Δ
slack_sdk/models/blocks/__init__.py	100.00% <100.00%> (ø)
slack_sdk/models/blocks/blocks.py	96.83% <100.00%> (+0.57%)	⬆️
slack_sdk/socket_mode/builtin/internals.py	73.68% <0.00%> (-0.44%)	⬇️

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[filmaj]