minor #3541 Implement template annotation for getExtension (mitelg)

This PR was merged into the 3.x branch.

Discussion
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Implement template annotation for `getExtension`

Hello there 🙂  👋

my first PR here 😉

This change would help to improve static analysis with tools like PHPStan and Psalm.

Commits
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110871d1 Implement template annotation for `getExtension` and `getRuntime`

src/Environment.php

@@ -557,6 +557,13 @@ class Environment
         $this->runtimeLoaders[] = $loader;
     }
 
+    /**
+     * @template TExtension of ExtensionInterface
+     *
+     * @param class-string<TExtension> $class
+     *
+     * @return TExtension
+     */
     public function getExtension(string $class): ExtensionInterface
     {
         return $this->extensionSet->getExtension($class);
@@ -565,9 +572,11 @@ class Environment
     /**
      * Returns the runtime implementation of a Twig element (filter/function/tag/test).
      *
-     * @param string $class A runtime class name
+     * @template TRuntime of object
      *
-     * @return object The runtime implementation
+     * @param class-string<TRuntime> $class A runtime class name
+     *
+     * @return TRuntime The runtime implementation
      *
      * @throws RuntimeError When the template cannot be found
      */