Avoid leaking TargetChangedArgs event handlers

[jnyrup]

Deregistering events via an anonymous delegate can be problematic.

See e.g.
https://www.jetbrains.com/help/rider/EventUnsubscriptionViaAnonymousDelegate.html
https://pvs-studio.com/en/docs/warnings/v3084/

Used the code below to verify that the memory dump diff after the fix no longer contained instances of TargetChangedArgs.

using System;
using System.Threading.Tasks;
using NUnit.Framework;

namespace PuppeteerSharp.Tests.BrowserContextTests;

public class EventHandlerLeaks
{
    [Test]
    public async Task Event_Handler_leaks()
    {
        GC.Collect(4, GCCollectionMode.Forced, true, true);
        GC.WaitForPendingFinalizers();

        ; // Take memory dump
        {
            var launcher = new Launcher();
            await using var browser = await launcher.LaunchAsync(new()
            {
                Protocol = ProtocolType.WebdriverBiDi,
                Browser = SupportedBrowser.ChromeHeadlessShell
            });
            for (var i = 0; i < 500; i++)
            {
                await using var context = await browser.CreateBrowserContextAsync();
            }

            browser.Disconnect();
            await browser.CloseAsync();
        }

        GC.Collect(4, GCCollectionMode.Forced, true, true);
        GC.WaitForPendingFinalizers();
        ; // Take memory dump and compare
    }
}

[kblok]

Good catch!