[FLINK-37035][release] Build doc for release-2.0 branch

Author: reswqa

.github/workflows/docs.yml

@@ -28,12 +28,9 @@ jobs:
       matrix:
         branch:
           - master
-          # Since release-2.0-preview doesn't have specific branch, use rc branch as workaround.
-          # This should be replaced to release-2.0 once it was released.
-          - release-2.0-preview1-rc1
+          - release-2.0
           - release-1.20
           - release-1.19
-          - release-1.18
     steps:
       - uses: actions/checkout@v3
         with: