[11.x] No need to redeclare variables

[lucasmichot]

This PR refactors the ServeCommand class by eliminating redundant redeclarations of variables, such as repeated instantiations of Stringable. Instead, a single $stringable variable is reused throughout the method. This change simplifies the code, improves readability, and slightly optimizes performance by avoiding repeated object creation.

[kerwin-wildsea]

I wanted to create a Pull Request which would add a test to cover the error occurred in the Serve command. In this case, when a line unrelated to the port was in the outputBuffer. But looking at the existing tests in: ServeCommandLogParserTest.php only the function static::getRequestPortFromLine($line) is covered. Not the behaviour around it.

I don't really see how to easily add a test for this behaviour.