bug #15202 [Security] allow to use `method` in XML configs (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
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[Security] allow to use `method` in XML configs

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Before this change, you always had to use the `methods` key which is
inconsistent compared to other options like `roles` and `ips` for which
it was possible to use their singular versions.

Commits
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9b0dfd4 [Security] allow to use `method` in XML configs

src/Symfony/Bundle/SecurityBundle/DependencyInjection/MainConfiguration.php

@@ -158,6 +158,7 @@ class MainConfiguration implements ConfigurationInterface
                     ->cannotBeOverwritten()
                     ->prototype('array')
                         ->fixXmlConfig('ip')
+                        ->fixXmlConfig('method')
                         ->children()
                             ->scalarNode('requires_channel')->defaultNull()->end()
                             ->scalarNode('path')