Fix benchmark workflow: It should execute the benchmark script.

[sea212]

Fix benchmark workflow: It should execute the benchmark script. This way we can execute the script once per release to add new weights.

[sea212]

I realized that we need two scripts:

1. One script triggers when the benchmark label is set. It only respects our own pallets stored in the folder zrml. The label should always be set when the pallet logic changes, such that the weights are always up to date and can be used by other projects
2. A second script triggers manually. The bot will execute the benchmark script and benchmark all pallets, including external pallets. It will open a PR to update the weights. This will be used to prepare releases.

[sea212]

Automatic benchmarks of all pallets once per release are sufficient for now. I think it makes more sense to shift the responsibility of ensuring up to date weights to the projects that use the pallets, especially as they might use other reference hardware.