[zend-ldap]: fix failing tests due to changes in bitnami/openldap:2.5

restore expected message to the previous version
https://github.com/zf1s/zf1/pull/159/files#diff-10a1b3c35fa477d1ad544c164800886583a4162bf83154247e986d59da216ff5L184

tests/Zend/Ldap/BindTest.php

@@ -181,7 +181,7 @@ public function testRequiresDnWithoutDnBind()
         } catch (Zend_Ldap_Exception $zle) {
             /* Note that if your server actually allows anonymous binds this test will fail.
              */
-            $this->assertContains('No object found for', $zle->getMessage());
+            $this->assertContains('Failed to retrieve DN', $zle->getMessage());
         }
     }