Update to .NET SDK 9.0.300

[rainersigwald]

We should update the .NET SDK we use to build this repo. The current version is 9.0.300, but we're using an older one:

msbuild/global.json

Line 6 in 4ad4624

"dotnet": "9.0.106",

We should update that global.json value to 9.0.300 and run builds. If any new errors come up, we need to fix them.

[rainersigwald]

@Copilot can we actually update to 9.0.301 since it's out now?