Build docs for 1.9.0rc4

Author: foosel

.github/workflows/docs.yaml

@@ -23,7 +23,7 @@ jobs:
             mermaid: "0.6.3"
             jinja: "3.0.3"
             mermaid_fix: "true"
-          - version: "1.9.0rc3"
+          - version: "1.9.0rc4"
             source: "tags"
             python: "3.7"
             sphinx: "4.5.0"