minor #32928 [HttpClient] use "idle" instead of "inactivity" when telling about the timeout option (nicolas-grekas)

This PR was merged into the 4.3 branch.

Discussion
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[HttpClient] use "idle" instead of "inactivity" when telling about the timeout option

| Q             | A
| ------------- | ---
| Branch?       | 4.3
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

I feel like this might be easier to understand.
This is also the word I used in the doc.

Commits
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d2c4bf0da8 [HttpClient] use "idle" instead of "inactivity" when telling about the timeout option

Author: fabpot

DependencyInjection/Configuration.php

@@ -1348,7 +1348,7 @@ private function addHttpClientSection(ArrayNodeDefinition $rootNode)
                                     ->info('A comma separated list of hosts that do not require a proxy to be reached.')
                                 ->end()
                                 ->floatNode('timeout')
-                                    ->info('Defaults to "default_socket_timeout" ini parameter.')
+                                    ->info('The idle timeout, defaults to the "default_socket_timeout" ini parameter.')
                                 ->end()
                                 ->scalarNode('bindto')
                                     ->info('A network interface name, IP address, a host name or a UNIX socket to bind to.')