CI: update lint workflow actions

[jackspiering]

Description

Update the lint workflow to current action releases:

• Upgrade actions/checkout from v6 to v7.
• Upgrade rvben/rumdl from v0.2.41 to v0.2.73.

Related Issues

• None.

Verification

• rumdl check --config .markdownlint.yml services/ - passed with no issues in 122 files.
• git diff --check — passed.
• actionlint and yamllint were unavailable in the local environment. GitHub Actions will validate the workflow in the draft PR.

Checklist

• I have performed a self-review of my code and followed the templates structure.
• I have added verification that the stack works as expected.
• I have updated necessary documentation (e.g. frontpage README.md ).
• I have selected the correct label(s) for this PR.

Additional Context

• None.