minor #12398 [Cache] Improved the example about cache tags (pavelmaca, javiereguiluz)

This PR was merged into the 4.3 branch.

Discussion
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[Cache] Improved the example about cache tags

This continues the work started in #12181.

Commits
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f9d438f Fixed code
2651f92 [Cache] Improved the example about cache tags
ce0c625 [Cache] Fix example for using cache tags with TagAwareCacheInterface

Author: javiereguiluz

cache.rst

@@ -489,23 +489,33 @@ the same key could be invalidate with one function call::
     use Symfony\Contracts\Cache\ItemInterface;
     use Symfony\Contracts\Cache\TagAwareCacheInterface;
 
-    // using autowiring
-    public function listProducts(TagAwareCacheInterface $pool)
+    class SomeClass
     {
-        $value0 = $pool->get('item_0', function (ItemInterface $item) {
-            $item->tag(['foo', 'bar']);
+        private $myCachePool;
 
-            return 'debug';
-        });
+        // using autowiring to inject the cache pool
+        public function __construct(TagAwareCacheInterface $myCachePool)
+        {
+            $this->myCachePool = $myCachePool;
+        }
 
-        $value1 = $pool->get('item_1', function (ItemInterface $item) {
-            $item->tag('foo');
+        public function someMethod()
+        {
+            $value0 = $this->myCachePool->get('item_0', function (ItemInterface $item) {
+                $item->tag(['foo', 'bar']);
 
-            return 'debug';
-        });
+                return 'debug';
+            });
 
-        // Remove all cache keys tagged with "bar"
-        $pool->invalidateTags(['bar']);
+            $value1 = $this->myCachePool->get('item_1', function (ItemInterface $item) {
+                $item->tag('foo');
+
+                return 'debug';
+            });
+
+            // Remove all cache keys tagged with "bar"
+            $this->myCachePool->invalidateTags(['bar']);
+        }
     }
 
 The cache adapter needs to implement :class:`Symfony\\Contracts\\Cache\\TagAwareCacheInterface``