Creating checkpoint on Win/Mac fails if no package binaries available on MRAN

[hongooi73]

This is with the pkgdepends/pkgcache chain. Due to r-lib/pkgcache#38

[hongooi73]

Workaround is to specify a value for r_version for which binaries are available.

[hongooi73]

Other workaround: specify create_checkpoint(*, config=list(platforms="source"))