ci: rename style_guide_path to additional_instructions_path (#267)

Tracks the upstream rename in alexanderlhicks/lean-summary-workflow.
The input semantics are unchanged for this fork — the new name better
reflects that the file passed in can be any deployment-supplied
instructions, not just a style guide.

Merge ordering: the upstream lean-summary-workflow PR renaming the
input must land before this PR.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: alexanderlhicks

.github/workflows/summary.yml

@@ -27,6 +27,6 @@ jobs:
           github_repository: ${{ github.repository }}
           pr_number: ${{ github.event.pull_request.number }}
           # Optional:
-          style_guide_path: 'CONTRIBUTING.md'
+          additional_instructions_path: 'CONTRIBUTING.md'
           validate_title: 'true'
           # upstream_path: 'ToMathlib/'