ci(docs): run documentation build on every pull request

Remove the paths filter from the pull_request trigger so the required
Documentation build check always reports, matching Arduino_Core_STM32.
The push trigger keeps its paths filter.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: fpistm

.github/workflows/docs-check.yml

@@ -2,12 +2,6 @@ name: Documentation build
 
 on:
   pull_request:
-    paths:
-      - Doxyfile
-      - docs/**
-      - src/**
-      - mkdocs.yml
-      - .github/workflows/docs-check.yml
   push:
     branches:
       - main