add php 7.3 back to tests, seeing as Laravel still supports it as minimum for now

Author: michaeldyrynda

.github/workflows/run-tests.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php: [8.0, 7.4]
+        php: [8.0, 7.4, 7.3]
         dependency-version: [prefer-lowest, prefer-stable]
 
     name: P${{ matrix.php }} - L${{ matrix.laravel }} ${{ matrix.dependency-version }} - ${{ matrix.os }}