Switch Windows CI back to release pak once it supports Windows arm64 binaries #1471

#1467 set pak-version: devel for r-lib/actions/setup-r-dependencies in .github/workflows/test-windows.yml. Once a pak release includes the fix below, remove that line so Windows CI goes back to release pak.

Why we use dev pak

On windows-11-arm, the R installation that r-lib/actions/setup-r provides is the community Windows ARM64 build from r-devel/windows-arm64. Its etc/repositories sets CRAN to https://cran.r-universe.dev and marks it as having Windows binaries. setup-r keeps that repo.

pak 0.11.1 doesn't recognize R 4.6's Windows arm64 binary package type, so it treats r-universe as source-only and builds every R package from source (~20 min, mostly stringi). Because of r-lib/pkgdepends#486, pak also never counts those source-built packages as up to date, so the restored R package cache is ignored and the build happens on every run.

Dev pak (0.11.1.9000) includes r-lib/pkgcache#142 ("pkgcache now supports the custom binary package types of R 4.6.0 and later"). It installs r-universe's arm64 binaries, and the step takes under a minute.

The full investigation is in #1467. The same problem and workaround came up in stan-dev/cmdstanr#1304.

When to switch back

When a pak release's NEWS includes the pkgcache change above (custom binary package types for R 4.6+):

1. Remove the pak-version: devel line, and the comment above it, from .github/workflows/test-windows.yml.
2. Check the windows-11-arm job's "Install R Packages Required For Tests" step:
   • The "Repo status" group lists https://cran.r-universe.dev with platform aarch64-w64-mingw32-windows.binary.arm64, not only source.
   • The install plan has no [bld] tags, and the step takes about a minute, not about 20.