_sign-pkg-cosign.sh: use long-form option [ci skip]

`--yes=true` also works.

I found the cosign help screen misleading, `--yes=false` is the default,
meaning to do ask the Y/N question:
````
    -y, --yes=false:
        skip confirmation prompts for non-destructive operations
```

Author: vszakats

_sign-pkg-cosign.sh

@@ -15,7 +15,7 @@ if [ -n "${COSIGN_PKG_KEY:-}" ] && \
   file="$1"
   echo "Package signing with cosign: '${file}'"
   tr -d '\n' <<EOF | \
-  cosign sign-blob -y --key="${COSIGN_PKG_KEY}" --new-bundle-format=true --bundle="${file}".sigstore "${file}"
+  cosign sign-blob --yes --key="${COSIGN_PKG_KEY}" --new-bundle-format=true --bundle="${file}".sigstore "${file}"
 ${COSIGN_PKG_KEY_PASS}
 EOF
   chmod 0644 "${file}".sigstore  # cosign creates it with 0600