minor #43903 Fix more generic types (derrabus)

This PR was merged into the 5.4 branch.

Discussion
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Fix more generic types

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | N/A
| License       | MIT
| Doc PR        | N/A

Some changes I wanted to push to #42471, but then it got merged already. 😇

Commits
-------

c54d61e9af Fix more generic types

Author: fabpot

Kernel.php

@@ -58,7 +58,7 @@ class_exists(ConfigCache::class);
 abstract class Kernel implements KernelInterface, RebootableInterface, TerminableInterface
 {
     /**
-     * @var BundleInterface[]
+     * @var array<string, BundleInterface>
      */
     protected $bundles = [];
 

KernelInterface.php

@@ -31,7 +31,7 @@ interface KernelInterface extends HttpKernelInterface
     /**
      * Returns an array of bundles to register.
      *
-     * @return iterable<BundleInterface>
+     * @return iterable<mixed, BundleInterface>
      */
     public function registerBundles();
 
@@ -55,7 +55,7 @@ public function shutdown();
     /**
      * Gets the registered bundle instances.
      *
-     * @return BundleInterface[]
+     * @return array<string, BundleInterface>
      */
     public function getBundles();