[TASK] Block installations on unsupported higher PHP versions

We want Composer to be able to figure out which versions of which
libraries it can install on which version of PHP.

To make this possible, we should only allow installations on PHP
versions that we know to work.

This is the v8.x backport of #691.

Author: oliverklee

CHANGELOG.md

@@ -11,6 +11,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ### Changed
 
+- Block installations on unsupported higher PHP versions (#691)
+
 ### Deprecated
 
 ### Removed

composer.json

@@ -23,7 +23,7 @@
         }
     ],
     "require": {
-        "php": ">=5.6.20",
+        "php": "^5.6.0 || ^7.0.0 || ~8.0.0 || ~8.1.0 || ~8.2.0 || ~8.3.0 || ~8.4.0",
         "ext-iconv": "*"
     },
     "require-dev": {