Disable issue auto-filing for Cobalt-based benchmarks

[Copilot]

Cobalt-based benchmark results are too noisy for automated regression filing, similar to Azure-based machines.

RegressionBot Configuration

• Added [cC]obalt to the trend benchmark exclusion rules regex in build/regressions.config.yml to filter out Cobalt-hosted benchmark noise during regression checks.

sources:
  - name: Trends 
    table: TrendBenchmarks
    rules:
      # ...
      - exclude: '[aA]zure|[cC]obalt|Cloud|Idna'

[sebastienros]

The last change was made by the coding agent and requires additional review.

@EgorBo mentioned that issue last week :/ I started the copilot session and approved, then 1 more approval should be sufficient but it's not