JWK `key_ops` should be an array

[deevus]

From the RFC:

The "key_ops" (key operations) parameter identifies the operation(s)
for which the key is intended to be used. The "key_ops" parameter is
intended for use cases in which public, private, or symmetric keys
may be present.

Its value is an array of key operation values.

dart-cryptography/jwk/lib/jwk_plus.dart

Lines 118 to 119 in 211250a

	/// Operations.
	final String? keyOps;