ci: bump docs-validation job timeout to 240 minutes (wheels-dev#2464)

Bumps `timeout-minutes` from 90 to 240 so the View Helpers section
(88 functions, ~140 min projected at ~5 turns × ~30s/turn + ~3 min
brew/Node setup) can complete in a single dispatch instead of
requiring 3 re-runs that each pay the setup overhead.

Smaller sections (the previous 7) all finished well under 90 min, so
this change only affects the one outlier and is otherwise inert.

https://claude.ai/code/session_014puccJJixwdjRgMx7mPLmz

Co-authored-by: Claude <noreply@anthropic.com>

Author: bpamiri

.github/workflows/docs-validation.yml

@@ -48,7 +48,7 @@ concurrency:
 jobs:
   validate:
     runs-on: ubuntu-latest
-    timeout-minutes: 90
+    timeout-minutes: 240
 
     steps:
       - name: Checkout dispatching ref