Fix benchmarks (#444)

Author: dcherian

.github/workflows/benchmarks.yml

@@ -10,7 +10,7 @@ jobs:
     # if: ${{ contains( github.event.pull_request.labels.*.name, 'run-benchmark') && github.event_name == 'pull_request' || github.event_name == 'workflow_dispatch' }}  # Run if the PR has been labelled correctly.
     if: ${{ github.event_name == 'pull_request' || github.event_name == 'workflow_dispatch' }} # Always run.
     name: Linux
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     env:
       ASV_DIR: "./asv_bench"