Removed PHP 8.0

The version of phpunit we currently need to use for php 5.6 compatibility doesn’t work on php 8.0.

Author: barnabywalters

.github/workflows/main.yml

@@ -11,7 +11,7 @@ jobs:
 
     strategy:
       matrix:
-        php: ['5.6', '7.3', '7.4', '8.0']
+        php: ['5.6', '7.3', '7.4']
 
     runs-on: ubuntu-latest