kernelCTF: GHA: vuln-verify: faster checkout, fix gzip upload, less noisy cache logs

.github/workflows/kernelctf-vuln-verify.yaml

@@ -31,24 +31,13 @@ jobs:
         with:
           credentials_json: '${{ secrets.KERNELCTF_GCS_SA_KEY }}'
 
-      - name: Checkout PR
-        uses: actions/checkout@v4
-        with:
-          ref: ${{ env.PR_REF }}
-          path: pr
-          sparse-checkout: pocs/linux/kernelctf/**
-          sparse-checkout-cone-mode: false
-      
-      - name: List PR contents
-        run: find pr
-
       - name: Determine submission folder
         id: determine_folder
         run: |
           FILES=$(gh pr view $PR_NUM --json files --jq '.files[] | .path')
           echo "Files in PR:"
           echo "$FILES"
-          
+
           POC_FOLDER=$(echo "$FILES" | grep '^pocs/linux/kernelctf/' | cut -d/ -f1-4 | sort -u)
           if [ $(echo "$POC_FOLDER" | grep -c .) -ne 1 ]; then
             echo "Exactly one PoC folder must be found in pocs/linux/kernelctf/, but found:"
@@ -64,6 +53,18 @@ jobs:
           echo "folder=$POC_FOLDER" >> $GITHUB_OUTPUT
           echo "Found PoC folder: $POC_FOLDER"
 
+      - name: Checkout PR
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ env.PR_REF }}
+          path: pr
+          sparse-checkout: "${{ steps.determine_folder.outputs.folder }}"
+          sparse-checkout-cone-mode: true
+          fetch-depth: 1
+
+      - name: List PR contents
+        run: find pr
+
       - name: Checkout kernel-research
         uses: actions/checkout@v4
         with: