docs: Fix format issue in rbac.md (#16521) (#16540)

Wrongly placed horizontal line (`----`) was formatting code-block as a header. Fixed it with a necessary line break

Signed-off-by: Elouan Keryell-Even <[email protected]>
Co-authored-by: Elouan Keryell-Even <[email protected]>

Author: gcp-cherry-pick-bot[bot]

docs/operator-manual/rbac.md

@@ -155,6 +155,7 @@ data:
 
     g, your-github-org:your-team, role:org-admin
 ```
+
 ----
 
 Another `policy.csv` example might look as follows: