Only run the playground release job on release (#4636)

.github/workflows/docs.yaml

@@ -1,9 +1,9 @@
 name: mkdocs
 
 on:
+  workflow_dispatch:
   release:
     types: [ published ]
-  workflow_dispatch:
 
 jobs:
   mkdocs:

.github/workflows/playground.yaml

@@ -2,8 +2,8 @@ name: "[Playground] Release"
 
 on:
   workflow_dispatch:
-  push:
-    branches: [main]
+  release:
+    types: [ published ]
 
 env:
   CARGO_INCREMENTAL: 0