Enable transitive pins and bump System.Text.Json

[MattKotsenas]

Fix broken build due to NU1903.

To do so I:

1. Enabled transitive pinning
2. Bumped System.Text.Json to 6.0.10 for .NET 6.0
3. Bumped System.Text.Json to 8.0.5 for all other TFMs

This mirrors the existing logic, but it isn't entirely clear to me why it was this way to begin with.

Comparing packages before and after, the version is bumped as expected (and no other package dependencies change) except the .NET 6.0 TFM now has a dependency on System.Text.Json.

[MattKotsenas]

Here's the side-by-side (Old vs. New) in NuGet Package Explorer for this change

You know this area much better than me, so feel free to do what you please. Just helping out where I can since I already have the project open :)

[MattKotsenas]

Same as #305, so pick which one you like better and close the other one ;)

[jeffkl]

I'm not ready for transitive pinning just yet 😄