release: update cosign to 1.3.1 (#1038)

Signed-off-by: Carlos Panato <[email protected]>

Author: cpanato

release/cloudbuild.yaml

@@ -32,7 +32,7 @@ steps:
     echo "Checking out ${_TOOL_REF}"
     git checkout ${_TOOL_REF}
 
-- name: 'gcr.io/projectsigstore/cosign:1.3.0@sha256:65de2f3f2844815ed20ab939319e3dad4238a9aaaf4893b22ec5702e9bc33755'
+- name: 'gcr.io/projectsigstore/cosign:v1.3.1@sha256:3cd9b3a866579dc2e0cf2fdea547f4c9a27139276cc373165c26842bc594b8bd'
   dir: "go/src/sigstore/cosign"
   args:
   - 'verify'