Check user/org repo limit instead of doer

[DrMaxNix]

This PR tries to finally fix the bug mentioned in #30011 and #15504, where the user repo limit is checked when creating a repo in an organization.

Fix #30011

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Please verify that this change makes sense, I don't know a lot about the gitea codebase, so I cannot overlook the security implications that this change will have for other parts of the code.

[TheFox0x7]

Change looks reasonable to me, though I'm also not an expert.

[wxiaoguang]

I think we need a complete fix like this: 8b48d86

Use CanCreateRepoIn , it should be clearer than before and won't be abused.

[wxiaoguang]

And let's add some tests: c654ade

[wxiaoguang]

fix merge conflict