Fix source reference for readme update

Author: codedmonkey

src/Package/PackageMetadataResolver.php

@@ -402,12 +402,8 @@ private function sanitize(?string $str): ?string
     private function updateReadme(Version $version, VcsDriverInterface $driver): void
     {
         try {
-            $composerInfo = $driver->getComposerInformation($driver->getRootIdentifier());
-            if (isset($composerInfo['readme']) && is_string($composerInfo['readme'])) {
-                $readmeFile = $composerInfo['readme'];
-            } else {
-                $readmeFile = 'README.md';
-            }
+            $composerInfo = $driver->getComposerInformation($version->getSource()['reference']);
+            $readmeFile = is_string($composerInfo['readme'] ?? null) ? $composerInfo['readme'] : 'README.md';
 
             $ext = substr($readmeFile, (int) strrpos($readmeFile, '.'));
             if ($ext === $readmeFile) {