Fix deprecation warnings

Author: LeoColomb

composer.lock

@@ -27,7 +27,7 @@ public function dumpFiles(Package $package, string $dir): array
         $paths = [];
 
         $this->filesystem->dumpFile(
-            $paths[] = "${dir}/composer.json",
+            $paths[] = "{$dir}/composer.json",
             $composerJsonContent
         );
 

src/Package/Writer.php

@@ -13,6 +13,8 @@
 
 class PackageTest extends TestCase
 {
+    private Package $builder;
+
     public Package $pkgA;
     public Package $pkgAAlpha;
     public Package $pkgB;