[ci] Stop per-PR cache copies from crowding the 10GB Actions cache quota (#17463)

.github/actions/restore-python/action.yml

@@ -35,6 +35,9 @@ runs:
       uses: astral-sh/setup-uv@11f9893b081a58869d3b5fccaea48c9e9e46f990 # v8.3.2
       with:
         enable-cache: true
+        # Pull request saves land in per-PR scopes nothing else can
+        # reuse; dev pushes seed the shared copy instead.
+        save-cache: ${{ github.event_name != 'pull_request' }}
         # Pin uv version so the action does not have to fetch the
         # manifest from raw.githubusercontent.com on every cache
         # miss; that fetch flakes on Windows runners.