Sync to 5.0.0-rc.1.20451.13 (release)

Commit 422fcb2a51c7616b0e2bbeb28c10309ed1b3b365

Remove NuGet.config for release

Enable buffering for split queries

Otherwise MARS is assumed by EF Core, which we don't support.

See https://github.com/dotnet/efcore/issues/21420

(cherry picked from commit ab5d62a447c3480de38b152ba14be12cce8e0b93)

Uninstall PG on Github Actions

Since PostgreSQL now comes pre-installed on the Github Actions image,
this messes up our custom installations.

(cherry picked from commit 91c243213c573081b419452ed3ebac5c48d620b8)

Remove NuGet.config for release

Synchronize to the released version of 5.0.0-preview2