Refactor Find Sources and fix bug when view a user who belongs to an unactive auth source (#27798)

The steps to reproduce it.

First, create a new oauth2 source.
Then, a user login with this oauth2 source.
Disable the oauth2 source.
Visit users -> settings -> security, 500 will be displayed.
This is because this page only load active Oauth2 sources but not all
Oauth2 sources.

services/auth/signin.go

@@ -11,6 +11,7 @@ import (
 	"code.gitea.io/gitea/models/db"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/services/auth/source/oauth2"
 	"code.gitea.io/gitea/services/auth/source/smtp"
 
@@ -85,7 +86,9 @@ func UserSignIn(ctx context.Context, username, password string) (*user_model.Use
 		}
 	}
 
-	sources, err := auth.AllActiveSources(ctx)
+	sources, err := auth.FindSources(ctx, auth.FindSourcesOptions{
+		IsActive: util.OptionalBoolTrue,
+	})
 	if err != nil {
 		return nil, nil, err
 	}