ci/github-script/bot: skip mergeability checks temporarily

This is an experiment and can be reverted a few days from now; if
the results are positive on GitHub’s end, then we may want to make
the merge conflict checks run less frequently than the rest of the
labelling tasks.

ci/github-script/bot.js

@@ -145,10 +145,22 @@ module.exports = async ({ github, context, core, dry }) => {
 
     // This API request is important for the merge-conflict label, because it triggers the
     // creation of a new test merge commit. This is needed to actually determine the state of a PR.
+    //
+    // NOTE (2025-12-15): Temporarily skipping mergeability checks here
+    // on GitHub’s request to measure the impact of the resulting ref
+    // writes on their internal metrics; merge conflicts resulting from
+    // changes to target branches will not have labels applied for the
+    // duration. The label should still be updated on pushes.
+    //
+    // TODO: Restore mergeability checks in some form after a few days
+    // or when we hear back from GitHub.
     const pull_request = (
       await github.rest.pulls.get({
         ...context.repo,
         pull_number,
+        // Undocumented parameter (as of 2025-12-15), added by GitHub
+        // for us; stability unclear.
+        skip_mergeability_checks: true,
       })
     ).data