Add support for Promises being returned by uninstall in Composer 2.1

src/Patches.php

@@ -124,6 +124,7 @@ public function checkPatches(Event $event) {
       }
 
       // Remove packages for which the patch set has changed.
+      $promises = array();
       foreach ($packages as $package) {
         if (!($package instanceof AliasPackage)) {
           $package_name = $package->getName();
@@ -135,10 +136,14 @@ public function checkPatches(Event $event) {
             || ($has_patches && $has_applied_patches && $tmp_patches[$package_name] !== $extra['patches_applied'])) {
             $uninstallOperation = new UninstallOperation($package, 'Removing package so it can be re-installed and re-patched.');
             $this->io->write('<info>Removing package ' . $package_name . ' so that it can be re-installed and re-patched.</info>');
-            $installationManager->uninstall($localRepository, $uninstallOperation);
+            $promises[] = $installationManager->uninstall($localRepository, $uninstallOperation);
           }
         }
       }
+      $promises = array_filter($promises);
+      if ($promises) {
+        $this->composer->getLoop()->wait($promises);
+      }
     }
     // If the Locker isn't available, then we don't need to do this.
     // It's the first time packages have been installed.