fix(ci): r-lib/actions/setup-r — replace fabricated SHA pin (#13)

Fake: e6be7f7e834ac48ec1e05de91168e99fc4f640e2 (gh api -> 422)
Real: a51a8012b0aab7c32ef9d19bf54da93f3254335e (r-lib/actions v2.12.0)

`r-lib/actions/setup-r` is a subpath action — the SHA pins the whole
r-lib/actions repo at the referenced commit, then the runner uses the
`setup-r/` subdir. Version comment `# v2` preserved (v2.12.0 is in the
v2 line).

Provenance: 2026-05-30 estate audit.

Author: hyperpolymath

.github/workflows/integration-tests.yml

@@ -36,7 +36,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
 
       - name: Set up R ${{ matrix.r-version }}
-        uses: r-lib/actions/setup-r@e6be7f7e834ac48ec1e05de91168e99fc4f640e2 # v2
+        uses: r-lib/actions/setup-r@a51a8012b0aab7c32ef9d19bf54da93f3254335e # v2.12.0
         with:
           r-version: ${{ matrix.r-version }}