test(renv): read lockfiles with renv::lockfile_read() for renv >= 1.2.4

[VincentGuyader]

Problem

CI R CMD check fails on ubuntu/macos (release + oldrel) with:

Error: don't know how to create a lockfile from an object of class 'list'

main itself is affected: its last green CI run predates the current renv release. This is a renv version incompatibility, not a code regression, and it is unrelated to any package source change.

Root cause

The NOT_CRAN-gated renv tests read a generated lockfile back through the internal renv:::lockfile(path) API. In renv 1.2.4 that entry point only accepts a manifest and errors on a normal lockfile, raising the message above at test-renv_create.R:128. Package source (R/create_renv.R) is unaffected: it only writes lockfiles via the exported renv::snapshot(), which works fine on 1.2.4.

Because these tests are skip_on_cran(), the CRAN incoming check and win-builder are unaffected (both are 0/0/0); only the full CI check surfaces it.

Fix

Test-only. Read lockfiles through the exported, stable renv::lockfile_read(), available since well before renv 1.2.2, which returns a renv_lockfile object exposing $Packages directly. Three mechanical replacements across the two renv test files:

• getFromNamespace("lockfile", "renv")(x) -> renv::lockfile_read(x)
• expect_s3_class(y, "renv_lockfile_api") -> expect_s3_class(y, "renv_lockfile")
• z$data()$Packages -> z$Packages

Verification

• Full test suite green under both renv 1.2.2 and 1.2.4 (86 tests, 0 failed, 0 error, 1 skipped).
• Red captured first under 1.2.4 (exact CI error), then green after the fix.
• No leftover old-API usages in tests/ or R/; no source change.

No NEWS entry: test-infrastructure only, not user-facing, and these tests are skip_on_cran().