Update deprecated option in benchmarks script

[manuelmauro]

What does it do?

When running run-benches-for-runtime.sh to generate the runtime weights, the following warning appears in the logs:

Using the chain spec instead of the runtime to generate the genesis state is deprecated. Please remove the `--chain`/`--dev`/`--local` argument, point `--runtime` to your runtime blob and set `--genesis-builder=runtime`. This warning may become a hard error any time after December 2024. 

This PR updates the script to use --runtime <runtime> instead of --chain=<chain-spec>.

What important points reviewers should know?

Is there something left for follow-up PRs?

What alternative implementations were considered?

Are there relevant PRs or issues in other repositories (Substrate, Polkadot, Frontier, Cumulus)?

What value does it bring to the blockchain users?

[github-actions]

WASM runtime size check:

Compared to target branch

Moonbase runtime: 2408 KB (no changes) 🚨

Moonbeam runtime: 2396 KB (no changes) ✅

Moonriver runtime: 2404 KB (no changes) 🚨

Compared to latest release (runtime-3401)

Moonbase runtime: 2408 KB (+376 KB compared to latest release) 🚨

Moonbeam runtime: 2396 KB (+384 KB compared to latest release) ⚠️

Moonriver runtime: 2404 KB (+392 KB compared to latest release) 🚨

[github-actions]

Coverage Report

@@                                Coverage Diff                                 @@
##           master   manuel/update-deprecation-in-benchmarks-script      +/-   ##
==================================================================================
- Coverage   74.58%                                           74.14%   -0.44%     
+ Files         377                                              380       +3     
+ Lines       96042                                            96672     +630     
==================================================================================
+ Hits        71632                                            71675      +43     
+ Misses      24410                                            24997     +587     

Files Changed	Coverage
/runtime/common/src/apis.rs	29.21% (+0.36%)	🔼
/runtime/moonbase/src/lib.rs	50.74% (+0.40%)	🔼
/runtime/moonbeam/src/lib.rs	44.95% (+0.52%)	🔼
/runtime/moonriver/src/lib.rs	45.17% (+0.52%)	🔼

Coverage generated Wed Jan 22 17:05:34 UTC 2025