Specify RC3 for 8.4

The latest version seems broken:

/usr/bin/php8.4: error while loading shared libraries: libxml2.so.2: cannot open shared object file: No such file or directory

Author: oschwald

.github/workflows/test.yml

@@ -14,7 +14,7 @@ jobs:
       matrix:
         arch: ["amd64", "i386"]
         operating-system: [ubuntu-latest]
-        php-versions: ['7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
+        php-versions: ['7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4.0RC3']
         php-extensions: ['bcmath', 'gmp']
     name: "PHP ${{ matrix.php-versions }} (with ${{ matrix.php-extensions }}) test on ${{ matrix.operating-system }}/${{ matrix.arch }}"
     steps: