JS CI: save performance metrics
In !9922 (closed) I've noticed that we don't have previous performance metrics from the JS CI. E.g. see pipeline https://gitlab.haskell.org/ghc/ghc/-/jobs/1357671#L5151
This is despite some nightly jobs passing successfully: e.g. https://gitlab.haskell.org/ghc/ghc/-/jobs/1354095
We should look into why we don't have these metrics.