Fix the curl for creating and verifying the headers

[umang8496]

reference-implementations/utilities/on_subscibe-service/java/Readme.md

Line 78 in 9787b66

--data-raw '{"value":{"test":"test"}},

reference-implementations/utilities/on_subscibe-service/java/Readme.md

Line 89 in 9787b66

--data-raw '{"value":{"test":"test"}},"public_key":"public_key","header":"Signature keyId=\"abc.com|ukid|ed25519\",algorithm=\"ed25519\",created=\"1712239689\",expires=\"1712539689\",headers=\"(created) (expires) digest\",signature=\"Gy5wiiJYGeNOBsiXJKo4OF7fSKR65zkxa/FJjgBgenmRplhq9vNewz/ivXDFegSnrdQK9U9T19Ta55J7Aa6RBw==\""

Remove the unnecessary } from the payload as it makes the curl invalid.