Fix Actions being enabled accidentally (#24802)
Regression of #24536. If the user doesn't explicitly disable Actions, it
will be enabled.
1. Gitea will call `loadRepositoryFrom` before `loadActionsFrom`.
https://github.com/go-gitea/gitea/blob/25d4f95df25dae5226e96e813dde87b071d9155e/modules/setting/setting.go#L234-L237
2. In `loadRepositoryFrom`,
`rootCfg.Section("actions").Key("ENABLED").MustBool(true)` will set
`actions.ENABLED` with `true`.
https://github.com/go-gitea/gitea/blob/25d4f95df25dae5226e96e813dde87b071d9155e/modules/setting/repository.go#L313-L315
3. In `loadActionsFrom`, `rootCfg.Section("actions")` will get a section
with Actions enabled.
https://github.com/go-gitea/gitea/blob/25d4f95df25dae5226e96e813dde87b071d9155e/modules/setting/actions.go#L23-L26
Although the cause of the problem was using `true` by copy-paste
mistake, it also surprised me that
**`rootCfg.Section("actions").Key("ENABLED").MustBool(true)` doesn't
only read, but also write.**
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