GH Actions: minor tweak

Since Composer 2.2.0, the `--ignore-platform-reqs` setting can be made more specific.

By using `--ignore-platform-req=php+` instead of `--ignore-platform-reqs`, only the upper bound for PHP platform requirements will be ignored, not _all_ platform requirements.

Ref: https://blog.packagist.com/composer-2-2/#-ignore-platform-req-improvements

Author: jrfnl

.github/workflows/run-tests.yml

@@ -89,7 +89,7 @@ jobs:
     - name: Install dependencies - ignore platform reqs
       if: ${{ matrix.php >= 8.3 }}
       run: |
-        composer update --${{ matrix.dependency-version }} --prefer-dist --no-progress --ignore-platform-reqs --no-interaction
+        composer update --${{ matrix.dependency-version }} --prefer-dist --no-progress --ignore-platform-req=php+ --no-interaction
 
     - name: Execute Unit Tests
       run: vendor/bin/phpunit