Add Dependabot ignore rule for serverless >=4

[Copilot]

Dependabot should not propose upgrades to serverless v4+. Adds an ignore rule to the npm package ecosystem config.

Changes

• .github/dependabot.yml: Added ignore entry under the npm package ecosystem:

ignore:
  - dependency-name: serverless
    versions:
      - '>= 4'

Original prompt

can you add a Dependabot ignore rule to the npm package config to ignore versions of serverless that are >=4. Don't put quotes around the dependency name and don't put [] around the version string, do put single quotes around the version string

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