v2 - STJ reference should use a range

[baywet]

OpenAPI.NET/src/Microsoft.OpenApi.Readers/Microsoft.OpenApi.Readers.csproj

Line 34 in 863faee

<PackageReference Include="System.Text.Json" Version="9.0.0" />

If we don't have any strict dependency on newer APIs it should be [8.0,10.0) since:

• net6 and 7 are EOL.
• this will allow people on net8 to upgrade if they desire.
• this will give us a change to review any breaking changes for net10 when it comes out.

[baywet]

Update, after further discussions, the range should be [8.0,)