Add synchronize to build_docs

Author: k-burt-uch

.github/workflows/docs.yaml

@@ -9,7 +9,7 @@ on:
       - 'docs/**'
   # Use push trigger since 'paths-ignore' are not respected as expected by 'on.pull_request.paths-ignore', see https://github.com/actions/runner/issues/2324
   pull_request:
-    types: [opened]
+    types: [opened, synchronize]
 
 jobs:
   build_docs: