Migrate from Coveralls to Codecov for coverage reporting, mirroring the changes made in brick/math#109.

Changes required

1. .github/workflows/ci.yml

In the phpunit job, make the following changes:

• In the "Run PHPUnit with coverage" step, change the clover output path from build/logs/clover.xml to clover.xml (and remove the mkdir -p build/logs line and the mkdir -p mkdir -p build/logs bug):

  - name: Run PHPUnit with coverage
    run: vendor/bin/phpunit --coverage-clover clover.xml
    if: ${{ matrix.php-version == env.COVERAGE_PHP_VERSION }}

• Replace the "Upload coverage report to Coveralls" step with:

  - name: Upload coverage to Codecov
    uses: codecov/codecov-action@v5
    env:
      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
    if: ${{ matrix.php-version == env.COVERAGE_PHP_VERSION }}

  (Remove the old step that runs vendor/bin/php-coveralls with COVERALLS_REPO_TOKEN.)

Here is the current full content of .github/workflows/ci.yml for reference:

name: CI

on:
  push:
  pull_request:

env:
  PSALM_PHP_VERSION: "8.4"
  COVERAGE_PHP_VERSION: "8.4"

jobs:
  psalm:
    name: Psalm
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v4
      - name: Setup PHP
        uses: shivammathur/setup-php@v2
        with:
          php-version: ${{ env.PSALM_PHP_VERSION }}
      - name: Install composer dependencies
        uses: ramsey/composer-install@v3
      - name: Run Psalm
        run: vendor/bin/psalm --show-info=false --find-unused-psalm-suppress --no-progress

  coding-standard:
    name: Coding Standard
    uses: brick/coding-standard/.github/workflows/coding-standard.yml@v2
    with:
      working-directory: "tools/ecs"

  phpunit:
    name: PHPUnit
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        php-version:
          - "8.1"
          - "8.2"
          - "8.3"
          - "8.4"
        deps:
          - "highest"
        include:
          - php-version: "8.1"
            deps: "lowest"
    steps:
      - name: Checkout
        uses: actions/checkout@v4
      - name: Setup PHP
        uses: shivammathur/setup-php@v2
        with:
          php-version: ${{ matrix.php-version }}
          coverage: xdebug
      - name: Install composer dependencies
        uses: ramsey/composer-install@v3
        with:
          dependency-versions: ${{ matrix.deps }}
      - name: Run PHPUnit
        run: vendor/bin/phpunit
        if: ${{ matrix.php-version != env.COVERAGE_PHP_VERSION }}
      - name: Run PHPUnit with coverage
        run: |
          mkdir -p mkdir -p build/logs
          vendor/bin/phpunit --coverage-clover build/logs/clover.xml
        if: ${{ matrix.php-version == env.COVERAGE_PHP_VERSION }}
      - name: Upload coverage report to Coveralls
        run: vendor/bin/php-coveralls --coverage_clover=build/logs/clover.xml -v
        env:
          COVERALLS_REPO_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        if: ${{ matrix.php-version == env.COVERAGE_PHP_VERSION }}

2. README.md

Replace the Coveralls badge with a Codecov badge:

• Remove:

  [![Coverage Status](https://coveralls.io/repos/github/brick/postcode/badge.svg?branch=master)](https://coveralls.io/github/brick/postcode?branch=master)
  

• Add:

  [![Coverage](https://codecov.io/github/brick/postcode/graph/badge.svg)](https://codecov.io/github/brick/postcode)
  

3. composer.json

Remove php-coveralls/php-coveralls from the require-dev section.