fix: improve dashboard loading performances (#7604)

Generating dashboard page takes too long when table `action` contains
many records and error log contains message like

```
2025/04/21 21:21:07 ...activities/action.go:470:GetFeeds() [W] [Slow SQL Query] SELECT `action`.* FROM `action` INNER JOIN `repository` ON `repository`.id = `action`.repo_id WHERE user_id=? AND is_deleted=? ORDER BY `action`.`created_unix` DESC LIMIT 20 [12 false] - 2m8.393454675s
```

This mod removes unnecessary inner join like proposed
in https://github.com/go-gitea/gitea/pull/32127

For complete solution index(user_id, is_deleted) for action table
should be created also like in https://github.com/go-gitea/gitea/pull/32333
(not included in this mod).

Related: https://github.com/go-gitea/gitea/pull/32127
Related: https://github.com/go-gitea/gitea/pull/32333
Author-Change-Id: IB#1160173

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Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7604
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Paweł Bogusławski <pboguslawski@noreply.codeberg.org>
Co-committed-by: Paweł Bogusławski <pboguslawski@noreply.codeberg.org>

models/activities/action.go

@@ -467,11 +467,8 @@ func GetFeeds(ctx context.Context, opts GetFeedsOptions) (ActionList, int64, err
 		return nil, 0, err
 	}
 
-	sess := db.GetEngine(ctx).Where(cond).
-		Select("`action`.*"). // this line will avoid select other joined table's columns
-		Join("INNER", "repository", "`repository`.id = `action`.repo_id")
-
 	opts.SetDefaultValues()
+	sess := db.GetEngine(ctx).Where(cond)
 	sess = db.SetSessionPagination(sess, &opts)
 
 	actions := make([]*Action, 0, opts.PageSize)