Update package:web_benchmarks dep. (#8530)
This change is in preparation of the removal of `--web-renderer=html`.
* Related: https://github.com/flutter/packages/pull/8103 (tooling change to remove the parameter from the benchmark runner)
* Related: https://github.com/flutter/flutter/issues/145954 (general thread)
## Tests
In this case, CI should continue normally. The change is just adopting a new major version of `package:web_benchmarks` that removed some public API (that wasn't used in devtools).
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