minor #20084 example function param 1 requires string (franzholz)

This PR was merged into the 6.4 branch.

Discussion
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example function param 1 requires string

An int causes a PHP error

argument #1 ($line) must be of type int, string given,

Commits
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4f733e0 example function param 1 requires string

components/var_dumper.rst

@@ -627,7 +627,7 @@ For example, to get a dump as a string in a variable, you can do::
 
     $dumper->dump(
         $cloner->cloneVar($variable),
-        function (int $line, int $depth) use (&$output): void {
+        function (string $line, int $depth) use (&$output): void {
             // A negative depth means "end of dump"
             if ($depth >= 0) {
                 // Adds a two spaces indentation to the line