Remove 8.3 whilst unstable in GH

Author: ben-xo

.github/workflows/testing.yml

@@ -5,7 +5,7 @@ jobs:
     strategy:
       matrix:
         operating-system: [ubuntu-latest, macos-11]
-        php-versions: ['7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
+        php-versions: ['7.3', '7.4', '8.0', '8.1', '8.2']
     runs-on: ${{ matrix.operating-system }}
     steps:
       - name: Setup PHP and extensions