CI: Fix phpstan analysis with decomposer

PHPUnit doesn't use PSR-0 or PSR-4, but a classmap autoloader,
and decomposer doesn't support those. Therefore we have to load
the dependencies manually when using decomposer :(

decomposer.json

@@ -18,9 +18,8 @@
     "PHPUnit": {
         "url": "https://github.com/sebastianbergmann/phpunit.git",
         "version": "10.5.38",
-        "psr4": {
-            "prefix": "PHPUnit",
-            "search-path": "/src/"
+        "psr0": {
+            "path": "/src/"
         }
     }
 }

tests/phpstan.autoload.inc.php

@@ -18,12 +18,23 @@
 }
 else
 {
-    // Load decomposer autoloade.
+    // Load decomposer autoloader.
     $autoload_file = $base . '/decomposer.autoload.inc.php';
 }
 
 require_once $autoload_file;
 
+if (file_exists($base . '/vendor/autoload.php') == FALSE)
+{
+    include_once 'Framework/MockObject/Runtime/Interface/Stub.php';
+    include_once 'Framework/MockObject/Runtime/Interface/MockObject.php';
+    include_once 'Framework/Assert.php';
+    include_once 'Framework/Reorderable.php';
+    include_once 'Framework/SelfDescribing.php';
+    include_once 'Framework/Test.php';
+    include_once 'Framework/TestCase.php';
+}
+
 // Define application config lookup path
 $paths = [
     get_include_path(),