Skip R install in vendoring GHA when already up to date

Co-authored-by: sbfnk <sebastian.funk@lshtm.ac.uk>

Author: sbfnk-bot

.github/workflows/check-primarycensored.yaml

@@ -19,15 +19,33 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
+      - name: Check if update needed
+        id: check-version
+        run: |
+          vendored_version=$(head -1 inst/stan/functions/primarycensored.stan | grep -oP '[\d.]+$')
+          cran_version=$(curl -s https://cran.r-project.org/package=primarycensored | grep -oP 'Version:</td>\s*<td>\K[^<]+')
+          echo "vendored=$vendored_version" >> "$GITHUB_OUTPUT"
+          echo "cran=$cran_version" >> "$GITHUB_OUTPUT"
+          if [ "$vendored_version" = "$cran_version" ]; then
+            echo "up_to_date=true" >> "$GITHUB_OUTPUT"
+            echo "Vendored version $vendored_version matches CRAN"
+          else
+            echo "up_to_date=false" >> "$GITHUB_OUTPUT"
+            echo "Vendored version $vendored_version != CRAN version $cran_version"
+          fi
+
       - uses: r-lib/actions/setup-r@v2
+        if: steps.check-version.outputs.up_to_date == 'false'
 
       - uses: r-lib/actions/setup-r-dependencies@v2
+        if: steps.check-version.outputs.up_to_date == 'false'
         with:
           install-pandoc: false
           packages: |
             any::primarycensored
 
       - name: Regenerate vendored Stan functions
+        if: steps.check-version.outputs.up_to_date == 'false'
         run: |
           library(primarycensored)
           stan_code <- pcd_load_stan_functions(
@@ -50,6 +68,7 @@ jobs:
         shell: Rscript {0}
 
       - name: Create Pull Request
+        if: steps.check-version.outputs.up_to_date == 'false'
         uses: peter-evans/create-pull-request@v8
         with:
           commit-message: Update vendored primarycensored Stan functions