Allow using LOG_DEPRECATIONS_WHILE_TESTING environment variable

This matches laravel/framework#49457 feature except Testbench still logs
deprecation by default and you can disable it by adding
`LOG_DEPRECATIONS_WHILE_TESTING=(false)`

Signed-off-by: Mior Muhammad Zaki <crynobone@gmail.com>

src/Bootstrap/HandleExceptions.php

@@ -99,5 +99,6 @@ protected function shouldIgnoreDeprecationErrors()
     {
         return ! class_exists(LogManager::class)
             || ! self::$app->hasBeenBootstrapped();
+            || Env::get('LOG_DEPRECATIONS_WHILE_TESTING', true) !== false;
     }
 }