[Openid-specs-ab] Issue #1729: explicitly type proof JWT (openid/connect)

[Kristina Yasuda]

New issue 1729: explicitly type proof JWT
https://bitbucket.org/openid/connect/issues/1729/explicitly-type-proof-jwt

Kristina Yasuda:

Following BCP, something like:

* `typ`: with value `vci+jwt`, which explicitly types the proof proof JWT as recommended in [Section 3.11](https://rfc-editor.org/rfc/rfc8725) of \[[RFC8725](https://www.rfc-editor.org/internet-drafts/draft-ietf-oauth-dpop-11.html#RFC8725)\].

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