Set SSH_PRIVATE_KEY env var so it can be used in the "if" statement.

Author: jonpugh

.github/workflows/operations.site.deploy.ddev.yml

@@ -110,6 +110,8 @@ jobs:
   deploy-code:
     name: Deploy Code
     runs-on: ${{ inputs.github_runs_on }}
+    env:
+      SSH_PRIVATE_KEY: ${{ secrets.SSH_PRIVATE_KEY }}
 
     steps:
 
@@ -121,9 +123,9 @@ jobs:
 
       # Enable SSH agent to allow preview sites to clone.
       - uses: webfactory/ssh-agent@v0.9.1
-        if: ${{ secrets.SSH_PRIVATE_KEY }}
+        if: ${{ env.SSH_PRIVATE_KEY }}
         with:
-          ssh-private-key: ${{ secrets.SSH_PRIVATE_KEY }}
+          ssh-private-key: ${{ env.SSH_PRIVATE_KEY }}
 
       - name: Clone code
         env: