docs: find broken links using github-action-markdown-link-check

[rusackas]

SUMMARY

Following up on https://github.com/apache/superset/pull/28424, using another (relatively deprecated) action, while we figure out if ASF will let us use the first one.

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

[rusackas]

Wow, this takes FOREVER.

[rusackas]

closing in favor of https://github.com/apache/superset/pull/28424 which is much faster, and more sensible to config.