[nfc] Genericize pandoc versioning in CI

Signed-off-by: Schuyler Eldridge <[email protected]>

.github/workflows/pandoc.yml

@@ -9,6 +9,10 @@ on:
     branches:
       - main
 
+env:
+  pandoc-version: 3.1.8
+  pandoc-crossref-version: v0.3.17.0
+
 jobs:
   markdown-to-pdf:
     runs-on: ubuntu-22.04
@@ -24,8 +28,8 @@ jobs:
         shell: bash
         run: |
           mkdir -p usr/bin
-          wget https://github.com/jgm/pandoc/releases/download/3.1.8/pandoc-3.1.8-linux-amd64.tar.gz -O - | tar -zx -C usr/bin --strip-components 2
-          wget https://github.com/lierdakil/pandoc-crossref/releases/download/v0.3.17.0/pandoc-crossref-Linux.tar.xz -O - | tar -Jx -C usr/bin
+          wget https://github.com/jgm/pandoc/releases/download/${{ env.pandoc-version }}/pandoc-${{ env.pandoc-version }}-linux-amd64.tar.gz -O - | tar -zx -C usr/bin --strip-components 2
+          wget https://github.com/lierdakil/pandoc-crossref/releases/download/${{ pandoc-crossref-version }}/pandoc-crossref-Linux.tar.xz -O - | tar -Jx -C usr/bin
           echo "$(pwd)/usr/bin" >> $GITHUB_PATH
       - name: "Check Formatting"
         shell: bash