session_info() should include value of osVersion

[wch]

On Windows, session_info() reports os as follows:

 os       Windows 10 x64              

It would be helpful if it reported the value of osVersion, which is a bit more detailed:

> osVersion
[1] "Windows 10 x64 (build 18363)"

This information would have been helpful for debugging an issue with GitHub Actions that @schloerke and I encountered recently.

Note that on a Mac, there's no difference between session_info() and osVersion. I think the same is true for Linux.

 os       macOS Catalina 10.15.5      

> osVersion
[1] "macOS Catalina 10.15.5"