gh-1106: pin vale version in action to fix docs check

[paddyroddy]

Description

vale-cli/vale#1105 is causing the documentation action to fail, by pinning vale it passes.

Closes: #1106

Checks

• Is your code passing linting?
• Is your code passing tests?
• Have you added additional tests (if required)?
• Have you modified/extended the documentation (if required)?
• Have you added a one-liner changelog entry above (if required)?