chore: migrate GitHub Actions workflows to ubuntu-slim runners

[Copilot]

Replace ubuntu-latest with ubuntu-slim across all workflow files to reduce runner startup time and resource consumption.

Changes

• Updated runs-on field in 7 workflow files:
  • auto-assign-pr.yml
  • github-projects.yml
  • publish.yml
  • release-please.yml
  • rubocop-analysis.yml
  • ruby.yml
  • semantic-pr.yml

Each change is a single-line modification from runs-on: ubuntu-latest to runs-on: ubuntu-slim.

Original prompt

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This section details on the original issue you should resolve

<issue_title>chore: use ubuntu-slim for GitHub Actions runners</issue_title>
<issue_description>Replace ubuntu-latest with ubuntu-slim across all GitHub Actions workflows to reduce runner startup time and resource consumption.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes chore: use ubuntu-slim for GitHub Actions runners #66

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