CI: Always run latest version of js-benchmarks

Currently we default to GITHUB_REF for the checkout of js-benchmarks,
and if we've built up a large backlog of benchmark jobs to run, this can
mean we're running against a severely outdated version of js-benchmarks.

This new behavior allows us to see a failed js-benchmarks job, fix the
bug, and restart the failed job. This is important since we're testing a
specific commit and build from the upstream JS/WASM workflow.

.github/workflows/js-and-wasm-benchmarks.yml

@@ -36,6 +36,7 @@ jobs:
         with:
           repository: LadybirdBrowser/js-benchmarks
           path: js-benchmarks
+          ref: master
 
       - name: 'Install dependencies'
         if: ${{ matrix.os_name == 'Linux' }}