Don't set xdebug.default_enable in run-tests

This throws a deprecation warning in XDebug 3.

Closes GH-6324.

Author: bashkarev

run-tests.php

@@ -889,7 +889,7 @@ function write_information(): void
         'session' => ['session.auto_start=0'],
         'tidy' => ['tidy.clean_output=0'],
         'zlib' => ['zlib.output_compression=Off'],
-        'xdebug' => ['xdebug.default_enable=0','xdebug.mode=off'],
+        'xdebug' => ['xdebug.mode=off'],
         'mbstring' => ['mbstring.func_overload=0'],
     ];