Bump shivammathur/setup-php from 2.26.0 to 2.28.0

Bumps [shivammathur/setup-php](https://github.com/shivammathur/setup-php) from 2.26.0 to 2.28.0.
- [Release notes](https://github.com/shivammathur/setup-php/releases)
- [Commits](shivammathur/setup-php@2.26.0...2.28.0)

---
updated-dependencies:
- dependency-name: shivammathur/setup-php
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/on-pull-request.yml

@@ -26,7 +26,7 @@ jobs:
     name: PHP ${{ matrix.php }}; ${{ matrix.os }}
     steps:
       - name: Setup PHP
-        uses: shivammathur/setup-php@2.26.0
+        uses: shivammathur/setup-php@2.28.0
         with:
           php-version: ${{ matrix.php }}
           extensions: curl, json, mbstring, pcre