refactor: replace ActionRunnerToken.OwnerID & RepoID with optional.Option[int64] (#11601)

Currently:
- In the database, `NULL` is used in `action_runner_token.owner_id` & `.repo_id` to represent an absent value, as required by the foreign key
- In the code, `0` is used in `ActionRunnerToken.OwnerID` and `.RepoID` to represent an absent value

This PR replaces the `int64` fields with `optional.Option[int64]` which allows a single data type to be used for both cases, and removes the usage of the value `0` as a placeholder.

This change has a limited scope -- although `ActionRunnerToken` uses `NULL` values in the database, the related table `ActionRunner` still uses zero-values for `OwnerID` and `RepoID`.  This means a lot of code interacting with both of these tables still uses `0` values, such as the UI.  The changes here were stopped at a reasonable point to avoid cascading into all places that use the `ActionRunner` table.  (I'll continue this work in the future to enable foreign keys on `ActionRunner`, but likely after #11516 is completed to avoid serious conflict resolution problems.)

## 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 for Go changes

(can be removed for JavaScript changes)

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

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [ ] This change will be noticed by a Forgejo user or admin (feature, bug fix, performance, etc.). I suggest to include a release note for this change.
- [x] This change is not visible to a Forgejo user or admin (refactor, dependency upgrade, etc.). I think there is no need to add a release note for this change.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11601
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: Mathieu Fenniak <mathieu@fenniak.net>
Co-committed-by: Mathieu Fenniak <mathieu@fenniak.net>

routers/private/actions.go

@@ -15,6 +15,7 @@ import (
 	user_model "forgejo.org/models/user"
 	"forgejo.org/modules/json"
 	"forgejo.org/modules/log"
+	"forgejo.org/modules/optional"
 	"forgejo.org/modules/private"
 	"forgejo.org/modules/util"
 	"forgejo.org/services/context"
@@ -42,9 +43,18 @@ func GenerateActionsRunnerToken(ctx *context.PrivateContext) {
 		})
 	}
 
-	token, err := actions_model.GetLatestRunnerToken(ctx, owner, repo)
+	ownerID := optional.None[int64]()
+	if owner != 0 {
+		ownerID = optional.Some(owner)
+	}
+	repoID := optional.None[int64]()
+	if repo != 0 {
+		repoID = optional.Some(repo)
+	}
+
+	token, err := actions_model.GetLatestRunnerToken(ctx, ownerID, repoID)
 	if errors.Is(err, util.ErrNotExist) || (token != nil && !token.IsActive) {
-		token, err = actions_model.NewRunnerToken(ctx, owner, repo)
+		token, err = actions_model.NewRunnerToken(ctx, ownerID, repoID)
 		if err != nil {
 			errMsg := fmt.Sprintf("error while creating runner token: %v", err)
 			log.Error("NewRunnerToken failed: %v", errMsg)