Issue #3365180: Do not prevent UI install for PM warnings

src/Controller/BrowserController.php

@@ -78,6 +78,14 @@ class BrowserController extends ControllerBase {
       $active_plugins[$source->getPluginId()] = $source->getPluginDefinition()['label'];
     }
 
+    $pm_validation_errors = [];
+    $pm_validation_messages = [];
+    if ($ui_install_enabled) {
+      $pm_validate = $this->installReadiness->validatePackageManager();
+      $pm_validation_errors = $pm_validate['errors'];
+      $pm_validation_messages = $pm_validate['messages'];
+    }
+
     return [
       '#theme' => 'project_browser_main_app',
       '#attached' => [
@@ -101,7 +109,8 @@ class BrowserController extends ControllerBase {
             'current_sources_keys' => $current_sources_keys,
             'ui_install' => $ui_install_enabled,
             'stage_available' => $ui_install_enabled ? $this->installReadiness->installerAvailable() : FALSE,
-            'pm_validation' => $ui_install_enabled ? $this->installReadiness->validatePackageManager() : TRUE,
+            'pm_validation_errors' => count($pm_validation_errors) ? $pm_validation_errors : FALSE,
+            'pm_validation_messages' => count($pm_validation_messages) ? $pm_validation_messages : FALSE,
           ],
         ],
       ],