deps: update dependency cert-manager/cert-manager to v1.15.3 (#3689)

Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/actions/deploy-keptn-on-cluster/action.yml

@@ -64,7 +64,7 @@ runs:
       if: inputs.cert-manager-io-enabled == 'cert_manager_io_on'
       env:
         # renovate: datasource=github-releases depName=cert-manager/cert-manager
-        CERT_MANAGER_IO_VERSION: "v1.15.2"
+        CERT_MANAGER_IO_VERSION: "v1.15.3"
       shell: bash
       run: |
         kubectl apply -f https://github.com/cert-manager/cert-manager/releases/download/$CERT_MANAGER_IO_VERSION/cert-manager.yaml