doc: fixes wrong identation in a code block

[Brice187]

Checklist:

• [x] Commit Message Formatting: Commit titles and messages follow guidelines in the developer guide.
• [x] Reviewed the developer guide on Submitting a Pull Request
• [x] Pending release notes updated with breaking and/or notable changes for the next minor release. <- Just fixed a small typo, not worth to mention
• [x] Documentation has been updated, if necessary.
• [ ] Unit tests have been added, if necessary.
• [ ] Integration tests have been added, if necessary.

Small fix

Wrong formatting in the docs (You should not see 3 backticks and the reserved keyword YAML):

[mergify[bot]]

This pull request has merge conflicts that must be resolved before it can be merged. @Brice187 please rebase it. https://rook.io/docs/rook/latest/Contributing/development-flow/#updating-your-fork