Code Quality: Update source to show .NET Foundation copyright

[Lamparter]

Hi there (again)!
I noticed that the .NET Foundation copyright was missing from some source files and instead showed "IronPython Team", which isn't the official licenseholder specified in the LICENSE file in the root directory.
This is a small fix to change that to the .NET Foundation.

[slozier]

Thanks for the PR. I think this is fine although I try to avoid touching any licensing/copyright related stuff. @slide any chance you would remember the details regarding copyright when you did the onboarding with the .NET Foundation?

[slide]

I don't remember, sorry!

[Lamparter]

Submit a project | .NET Foundation

I'm going to imagine that IronPython would have been entered into the .NET Foundation under the Assignment model.

[slozier]

I'm going to imagine that IronPython would have been entered into the .NET Foundation under the Assignment model.

Yes, that's what I'm assuming as well but doesn't hurt to check.

[Lamparter]

Their website doesn't really display too much information about the project dotnetfoundation.org/projects/project-detail/DLR-IronPython2-IronPython3
There isn't really a place to ask for this sort of thing.

[Lamparter]

Regardless, the actual license states that the copyright holder is the .NET Foundation. @slozier would you mind reviewing this when you get a chance?