Fixes HTTP 500 when OIDC auto account linking (`ACCOUNT_LINKING=auto`)
requires local 2FA. `oauth2LinkAccount` set `linkAccount` in the session
before redirecting to 2FA but did not persist `linkAccountData`, so
`TwoFactorPost` failed with `not in LinkAccount session`. The manual
linking flow already stored both, this aligns auto-link with that
behavior.
Closes#38171
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Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>