CI: Update latest PHP version to last non-EOL version (#228)

When reading https://phpunit.de/announcements/phpunit-11.html I saw that since Feb 2 2024, 8.2 is the oldest still-supported PHP version.

Author: olleolleolle

.github/workflows/test-php.yml

@@ -24,7 +24,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php: ['8.1']
+        php: ['8.2']
         composer-mode: ['low-deps', 'high-deps']
 
     steps: