feature #14558 [PHPUnitBridge] Add deprecation log file option (michaelKaefer)

This PR was squashed before being merged into the 5.3-dev branch.

Discussion
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[PHPUnitBridge] Add deprecation log file option

For PR symfony/symfony#39098

Commits
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66d5f49 [PHPUnitBridge] Add deprecation log file option

Author: OskarStark

components/phpunit_bridge.rst

@@ -350,6 +350,16 @@ the compiling and warming up of the container:
 
     The ``--deprecations`` option was introduced in Symfony 5.1.
 
+Log Deprecations
+~~~~~~~~~~~~~~~~
+
+For turning the verbose output off and write it to a log file instead you can use
+``SYMFONY_DEPRECATIONS_HELPER='logFile=/path/deprecations.log'``.
+
+.. versionadded:: 5.3
+
+    The ``logFile`` option was introduced in Symfony 5.3.
+
 Write Assertions about Deprecations
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