GH-45377: [CI][R] Ensure install R on ubuntu-24.04 runner for R night…

…ly build jobs (#45464)

### Rationale for this change

Related to #45377.
As a result of the recent change in the ubuntu-latest GHA runner from ubuntu-22.04 to ubuntu-24.04, it appears that the tools included in the runner from the start have changed and jobs that assume R is already installed will now fail.
Installing R the job should now succeed.

### What changes are included in this PR?

### Are these changes tested?

### Are there any user-facing changes?

* GitHub Issue: #45377

Authored-by: eitsupi <50911393+eitsupi@users.noreply.github.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

.github/workflows/r_nightly.yml

@@ -60,7 +60,7 @@ jobs:
           repository: ursacomputing/crossbow
           ref: main
       - name: Set up Python
-        uses: actions/setup-python@42375524e23c412d93fb67b49958b491fce71c38 # v5.4.0
+        uses: actions/setup-python@42375524e23c412d93fb67b49958b491fce71c38 # v5.4.0
         with:
           cache: 'pip'
           python-version: 3.12
@@ -103,6 +103,7 @@ jobs:
           remote_key: ${{ secrets.NIGHTLIES_RSYNC_KEY }}
           remote_host_key: ${{ secrets.NIGHTLIES_RSYNC_HOST_KEY }}
       - run: tree repo
+      - uses: r-lib/actions/setup-r@v2
       - name: Build Repository
         shell: Rscript {0}
         run: |