[ci] Use local rsync-deployments action in docs workflow

Switch the two upload steps in .github/workflows/docs.yml from
burnett01/rsync-deployments to the locally-defined action added in the
previous commit. This fixes the nightly docs build, which currently
fails because the third-party action is not in the ASF allowed-actions
list.

This commit only touches main's workflow file. The cron trigger always
reads the workflow definition from the default branch, so release
branches do not need this change for the scheduled build to work --
they only need the local action committed alongside.

Author: GreatEugenius

.github/workflows/docs.yml

@@ -56,7 +56,7 @@ jobs:
           docker run --rm --volume "$PWD:/root/flink-agents" chesnay/flink-ci:java_8_11_17_21_maven_386 bash -c "cd /root/flink-agents && chmod +x ./tools/docs.sh && ./tools/docs.sh"
 
       - name: Upload documentation
-        uses: burnett01/rsync-deployments@7659d600d8bdd035bb5cdfba1d4bd0dd4a307ca6 # 8.0.2
+        uses: ./.github/actions/rsync-deployments
         with:
           switches: --archive --compress --delete
           path: docs/target/
@@ -68,7 +68,7 @@ jobs:
 
       - name: Upload documentation alias
         if: env.flink_alias != ''
-        uses: burnett01/rsync-deployments@7659d600d8bdd035bb5cdfba1d4bd0dd4a307ca6 # 8.0.2
+        uses: ./.github/actions/rsync-deployments
         with:
           switches: --archive --compress --delete
           path: docs/target/