bug: Forgejo Actions email notifications are opt-in (#8242)

* Add the `notify-email` column / NotifyEmail to ActionRun and set it:
  * services/actions/workflows.go `Dispatch`
  * services/actions/schedule_tasks.go `CreateScheduleTask`
  * services/actions/notifier_helper.go `handleWorkflows`
* Only send an email if the workflow has `enable-email-notifications: true` by having `MailActionRun` return immediately if `NotifyEmail` is false.
* Ignore or silently fail on `enable-email-notifications: true` parsing errors. Reporting such errors  belongs in workflow validation, not when it is evaluated for the notifications.
* Add unit and integration tests.

Refs: https://codeberg.org/forgejo/forgejo/issues/8187

## Checklist

The [contributor guide](https://forgejo.org/docs/next/contributor/) contains information that will be helpful to first time contributors. There also are a few [conditions for merging Pull Requests in Forgejo repositories](https://codeberg.org/forgejo/governance/src/branch/main/PullRequestsAgreement.md). You are also welcome to join the [Forgejo development chatroom](https://matrix.to/#/#forgejo-development:matrix.org).

### Tests

- I added test coverage for Go changes...
  - [x] in their respective `*_test.go` for unit tests.
  - [x] in the `tests/integration` directory if it involves interactions with a live Forgejo server.

### Documentation

- [x] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [x] I do not want this change to show in the release notes.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8242
Reviewed-by: Christopher Besch <mail@chris-besch.com>
Co-authored-by: Earl Warren <contact@earl-warren.org>
Co-committed-by: Earl Warren <contact@earl-warren.org>

models/actions/run.go

@@ -55,6 +55,7 @@ type ActionRun struct {
 	PreviousDuration time.Duration
 	Created          timeutil.TimeStamp `xorm:"created"`
 	Updated          timeutil.TimeStamp `xorm:"updated"`
+	NotifyEmail      bool
 }
 
 func init() {