minor symfony#37911 [Cache] fix expected exception message on PHP 8 (xabbuh)

This PR was merged into the 3.4 branch.

Discussion
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[Cache] fix expected exception message on PHP 8

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |

Commits
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2c9af57 fix expected exception messages on PHP 8

Author: fabpot

src/Symfony/Component/Cache/Tests/Adapter/MemcachedAdapterTest.php

@@ -71,7 +71,7 @@ public function testBadOptions($name, $value)
             $this->expectExceptionMessage('constant(): Couldn\'t find constant Memcached::');
         } else {
             $this->expectException('Error');
-            $this->expectExceptionMessage('Undefined class constant \'Memcached::');
+            $this->expectExceptionMessage('Undefined constant Memcached::');
         }
 
         MemcachedAdapter::createConnection([], [$name => $value]);

src/Symfony/Component/Cache/Tests/Simple/MemcachedCacheTest.php

@@ -81,7 +81,7 @@ public function testBadOptions($name, $value)
             $this->expectExceptionMessage('constant(): Couldn\'t find constant Memcached::');
         } else {
             $this->expectException('Error');
-            $this->expectExceptionMessage('Undefined class constant \'Memcached::');
+            $this->expectExceptionMessage('Undefined constant Memcached::');
         }
 
         MemcachedCache::createConnection([], [$name => $value]);