Update symfony/polyfill-php81 requirement from ^1.27 to ^1.28

Updates the requirements on [symfony/polyfill-php81](https://github.com/symfony/polyfill-php81) to permit the latest version.
- [Commits](symfony/polyfill-php81@v1.27.0...v1.28.0)

---
updated-dependencies:
- dependency-name: symfony/polyfill-php81
  dependency-type: direct:production
...

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

composer.json

@@ -22,7 +22,7 @@
         "psr/http-message": "^1.1",
         "slim/slim": "^4.12",
         "twig/twig": "^3.7",
-        "symfony/polyfill-php81": "^1.27"
+        "symfony/polyfill-php81": "^1.28"
     },
     "require-dev": {
         "phpunit/phpunit": "^9.6",