Add admin.apps.requests.cancel API method support

[seratch]

Summary

This pull request adds admin.apps.requests.cancel API method support to this SDK.

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 #1161 (cd30461) into main (f299906) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1161   +/-   ##
=======================================
  Coverage   86.66%   86.66%           
=======================================
  Files         110      110           
  Lines       10762    10771    +9     
=======================================
+ Hits         9327     9335    +8     
- Misses       1435     1436    +1     

Impacted Files	Coverage Δ
slack_sdk/web/async_client.py	84.91% <100.00%> (+0.04%)	⬆️
slack_sdk/web/client.py	86.32% <100.00%> (+0.04%)	⬆️
slack_sdk/web/legacy_client.py	86.03% <100.00%> (+0.04%)	⬆️
slack_sdk/socket_mode/builtin/internals.py	72.00% <0.00%> (-0.45%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f299906...cd30461. Read the comment docs.

[seratch]

@mwbrooks Thanks for checking this!