github/workflows: disable page job on pr

.github/workflows/user_project_ci.yml

diff --git a/.github/workflows/user_project_ci.yml b/.github/workflows/user_project_ci.yml
index 4840801..a39a0db 100644
--- a/.github/workflows/user_project_ci.yml
+++ b/.github/workflows/user_project_ci.yml
@@ -301,6 +301,7 @@
         key: ${{ runner.os }}-webgl-${{ github.run_id }}
 
   pages:
+    if: github.ref == 'main'    
     needs:
     - svg
     - webgl