fix: cosign 3 download url

Author: midnightercz

Dockerfile

@@ -52,7 +52,7 @@ RUN ARCH=$(uname -m) && \
     rm -f /tmp/cosign-linux-*.gz
 
 RUN ARCH=$(uname -m) && if [ "$ARCH" == "x86_64" ]; then ARCH=amd64; fi && \
-    curl -L https://github.com/sigstore/cosign/releases/download/${COSIGN3_VERSION}/cosign-linux-${ARCH} -o /usr/local/bin/cosign3 && \
+    curl -L https://github.com/sigstore/cosign/releases/download/v${COSIGN3_VERSION}/cosign-linux-${ARCH} -o /usr/local/bin/cosign3 && \
     chmod +x /usr/local/bin/cosign3