osxkeychain: store new attributes

osxkeychain: store new attributes

d208bfdfef (credential: new attribute password_expiry_utc, 2023-02-18)
and a5c76569e7 (credential: new attribute oauth_refresh_token,
2023-04-21) introduced new credential attributes but support was missing
from git-credential-osxkeychain.

Support these attributes by appending the data to the password in the
keychain, separated by line breaks. Line breaks cannot appear in a git
credential password so it is an appropriate separator.

Fixes the remaining test failures with osxkeychain:

    18 - helper (osxkeychain) gets password_expiry_utc
    19 - helper (osxkeychain) overwrites when password_expiry_utc
    changes
    21 - helper (osxkeychain) gets oauth_refresh_token

Signed-off-by: Bo Anderson <mail@boanderson.me>
Signed-off-by: Junio C Hamano <gitster@pobox.com>