Tag PR image build as latest before scanning

This is less effort than passing the tag across steps 🤷‍♂️

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>
(cherry picked from commit 378edb939d)
Signed-off-by: Brad Davidson <brad.davidson@rancher.com>

.github/workflows/trivy.yaml

@@ -27,11 +27,12 @@ jobs:
       run: |
         make local
         make package-image
+        make tag-image-latest
 
     - name: Run Trivy vulnerability scanner
       uses: aquasecurity/trivy-action@0.24.0
       with:
-        image-ref: 'rancher/k3s'
+        image-ref: 'rancher/k3s:latest'
         format: 'table'
         severity: "HIGH,CRITICAL"
         output: "trivy-report.txt"