Use an absolute path when resolving the composer vendor dir

Author: LukeTowers

src/Composer.php

@@ -347,7 +347,9 @@ public function setVendorDir(string $vendorDir): static
      */
     public function getComposerVendorDir(): string
     {
-        return rtrim($this->getVendorDir(), DIRECTORY_SEPARATOR)
+        return rtrim($this->getWorkDir(), DIRECTORY_SEPARATOR)
+            . DIRECTORY_SEPARATOR
+            . rtrim($this->getVendorDir(), DIRECTORY_SEPARATOR)
             . DIRECTORY_SEPARATOR
             . 'composer';
     }