Drop PHP < 7.4 support

This will allow us to use flexible heredocs in test,
as well as typed properties and other goodies.

https://www.php.net/releases/7_3_0.php
https://www.php.net/releases/7_4_0.php

.github/workflows/continuous-integration.yml

@@ -19,8 +19,6 @@ jobs:
     strategy:
       matrix:
         php:
-          - "7.2"
-          - "7.3"
           - "7.4"
           - "8.0"
           - "8.1"
@@ -65,7 +63,7 @@ jobs:
     strategy:
       matrix:
         php:
-          - "7.4"
+          - "8.0"
 
     steps:
       - name: "Checkout"
@@ -116,7 +114,7 @@ jobs:
     strategy:
       matrix:
         php:
-          - "7.2"
+          - "7.4"
 
     steps:
       - name: "Checkout"