[Bug] Disable deploy on fork repos

[mumupika]

I have noticed that a deployment failed triggered on my fork repo.
The deployment should only triggered on this repo but not on other forked repos for safety concerns.

You can have: deploy.yml modified to:

name: Deploy to GitHub Pages

on:
  push:
    branches: [main]
  # Allows you to run this workflow manually from the Actions tab on GitHub.
  workflow_dispatch:

# Allow this job to clone the repo and create a page deployment
permissions:
  contents: read
  pages: write
  id-token: write

jobs:
  build:
    runs-on: ubuntu-latest
    env:
      CPPDOC_SITE: https://cppdoc.cc
    steps:
      - name: Checkout source code
        uses: actions/checkout@v6
      - name: Build and upload artifacts
        uses: withastro/action@v5

  deploy:
    needs: build
    runs-on: ubuntu-latest
    # disable the fork repo deployment.
    if: github.repository == 'cppdoc-cc/cppdoc'
    environment:
      name: github-pages
      url: ${{ steps.deployment.outputs.page_url }}
    steps:
      - name: Deploy to GitHub Pages
        id: deployment
        uses: actions/deploy-pages@v4