Update action.yml (#266)

This pr updates action.yml 3p action aquasecurity/setup-trivy to use a
CSHA.

References

https://github.com/aquasecurity/setup-trivy


By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

Author: Miqueasher

.github/actions/image_scan/action.yml

@@ -32,7 +32,7 @@ runs:
     run: docker logout public.ecr.aws
 
   - name: Run Trivy vulnerability scanner on image
-    uses: aquasecurity/trivy-action@master
+    uses: aquasecurity/trivy-action@b6643a29fecd7f34b3597bc6acb0a98b03d33ff8 # v0.33.1
     with:
       image-ref: ${{ inputs.image-ref }}
       severity: ${{ inputs.severity }}