Remove PHP 5.6 from the unit test matrix

Author: stevegrunwell

.github/workflows/unit-tests.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-version: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
+        php-version: ['7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
     steps:
       - name: Checkout
         uses: actions/checkout@v4