Update tls13_enc.c
Update tls13_enc.c

Fix double + in hkdflabel declaration (FIXES #10675)
CLA: trivial

Reviewed-by: Matt Caswell <1fa2ef4755a9226cb9a0a4840bd89b158ac71391@openssl.org>
Reviewed-by: Kurt Roeckx <bb87b47479d83cec3c76132206933257ded727b2@roeckx.be>
Reviewed-by: Matthias St. Pierre <1910231d24f125aceac7850dc92279eee8d52323@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/10700)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl