Test postProcessingCommand adding a warning block

We want to add a note to each generated API doc for Random Beacon that informs
about contracts not being deployed on Mainnet. This commit tests the command for
adding the note.

.github/workflows/contracts-random-beacon-docs.yml

@@ -42,9 +42,11 @@ jobs:
       needs.docs-detect-changes.outputs.path-filter == 'true'
         || github.event_name == 'push'
         || github.event_name == 'workflow_dispatch'
-    uses: keep-network/ci/.github/workflows/reusable-solidity-docs.yml@main
+    # TODO: switch `post-processing-command` to `main` before merge
+    uses: keep-network/ci/.github/workflows/reusable-solidity-docs.yml@post-processing-command
     with:
       projectDir: /solidity/random-beacon
+      postProcessingCommand: find ./generated-docs -name "*.md" -type f -exec sed -i '3i \ **Warning:** This file documents a code which is not yet deployed to Mainnet. \ ' {} +
       publish: false
       addTOC: false
       commentPR: true