chore: get rid of build warnings

[mxschmitt]

This fixes:

/Users/maxschmitt/.nuget/packages/microsoft.codeanalysis.netanalyzers/7.0.3/build/Microsoft.CodeAnalysis.NetAnalyzers.targets(593,5): warning : The .NET SDK has newer analyzers with version '8.0.0' than what version '7.0.3' of 'Microsoft.CodeAnalysis.NetAnalyzers' package provides. Update or remove this package reference. [/Users/maxschmitt/Developer/playwright-dotnet/src/Playwright/Playwright.csproj]
CSC : warning SA0001: XML comment analysis is disabled due to project configuration (https://github.com/DotNetAnalyzers/StyleCopAnalyzers/blob/master/documentation/SA0001.md) [/Users/maxschmitt/Developer/playwright-dotnet/src/tools/Playwright.Tooling/Playwright.Tooling.csproj]
/Users/maxschmitt/Developer/playwright-dotnet/src/Playwright.Tests/BrowserContextRouteTests.cs(369,13): warning CS4014: Because this call is not awaited, execution of the current method continues before the call is completed. Consider applying the 'await' operator to the result of the call. [/Users/maxschmitt/Developer/playwright-dotnet/src/Playwright.Tests/Playwright.Tests.csproj::TargetFramework=net8.0]
/Users/maxschmitt/Developer/playwright-dotnet/src/Playwright.Tests/BrowserContextRouteTests.cs(366,20): warning CS1998: This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread. [/Users/maxschmitt/Developer/playwright-dotnet/src/Playwright.Tests/Playwright.Tests.csproj::TargetFramework=net8.0]
/Users/maxschmitt/Developer/playwright-dotnet/src/Playwright.Tests/PageRouteTests.cs(777,13): warning CS4014: Because this call is not awaited, execution of the current method continues before the call is completed. Consider applying the 'await' operator to the result of the call. [/Users/maxschmitt/Developer/playwright-dotnet/src/Playwright.Tests/Playwright.Tests.csproj::TargetFramework=net8.0]
/Users/maxschmitt/Developer/playwright-dotnet/src/Playwright.Tests/PageRouteTests.cs(774,20): warning CS1998: This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread. [/Users/maxschmitt/Developer/playwright-dotnet/src/Playwright.Tests/Playwright.Tests.csproj::TargetFramework=net8.0]
    9 Warning(s)