core: fix source_flow_manager throwing error when authenticated user attempts to re-authenticate with existing link (cherry-pick #12080)

[gcp-cherry-pick-bot[bot]]

Cherry-picked core: fix source_flow_manager throwing error when authenticated user attempts to re-authenticate with existing link (#12080)

Signed-off-by: Jens Langhammer jens@goauthentik.io

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.49%. Comparing base (b51d8d0) to head (eb0ba11). Report is 1 commits behind head on version-2024.10.

:white_check_mark: All tests successful. No failed tests found.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## version-2024.10 #12081 +/- ## =================================================== - Coverage 92.58% 92.49% -0.10% =================================================== Files 761 761 Lines 37844 37857 +13 =================================================== - Hits 35037 35014 -23 - Misses 2807 2843 +36 ``` | [Flag](https://app.codecov.io/gh/goauthentik/authentik/pull/12081/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=goauthentik) | Coverage Δ | | |---|---|---| | [e2e](https://app.codecov.io/gh/goauthentik/authentik/pull/12081/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=goauthentik) | `48.74% <7.69%> (-0.39%)` | :arrow_down: | | [integration](https://app.codecov.io/gh/goauthentik/authentik/pull/12081/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=goauthentik) | `24.89% <0.00%> (-0.01%)` | :arrow_down: | | [unit](https://app.codecov.io/gh/goauthentik/authentik/pull/12081/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=goauthentik) | `90.17% <100.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=goauthentik#carryforward-flags-in-the-pull-request-comment) to find out more.

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