Point the tracking-issue proof at the locked pytest command

#887 changed the test job to run uv run --frozen pytest tests/, so the
proof's recorded invocation no longer matched and the rules registry check
failed after the rebase.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: anth-volk

rules/registry.toml

@@ -1505,7 +1505,7 @@ project = "projects/policyengine-simulation-entry"
 test = "tests/test_pr_description_check.py::test_rule_proof_pr_tracking_issue"
 workflow = ".github/workflows/pr.yml"
 job = "test"
-invocation = "uv run pytest tests/"
+invocation = "uv run --frozen pytest tests/"
 
 [[rule]]
 id = "sim.process.same-repo-draft-prs"