chore(nilnil lint): resolve low-hanging fruit nilnil lint violations (#13230)

Some files excluded from the nilnil lint and listed in https://codeberg.org/forgejo/forgejo/issues/11261 contain no violations of the lint anymore. I removed them from the list. They are

- `routers/api/packages/container/auth.go`
- `routers/api/packages/nuget/auth.go`
- `routers/web/repo/setting/runners.go`
- `services/issue/commit.go`
- `services/migrations/onedev.go`

Other files contained lints that are triggered by returning `nil` for maps. This can be mitigated easily by returning `make(map[...]...)`. All except one of those return statements are already covered by tests. I list the ones that have coverage now, the statement that has no coverage was not changed.

### Tests for Go changes

- 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/13230
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>

models/activities/action_list.go

@@ -29,7 +29,7 @@ func (actions ActionList) getUserIDs() []int64 {
 
 func (actions ActionList) LoadActUsers(ctx context.Context) (map[int64]*user_model.User, error) {
 	if len(actions) == 0 {
-		return nil, nil
+		return make(map[int64]*user_model.User), nil
 	}
 
 	userIDs := actions.getUserIDs()

models/organization/org_user.go

@@ -123,13 +123,13 @@ func IsAnEligibleTeamMemberByID(ctx context.Context, uid int64) (bool, error) {
 
 func loadOrganizationOwners(ctx context.Context, users user_model.UserList, orgID int64) (map[int64]*TeamUser, error) {
 	if len(users) == 0 {
-		return nil, nil
+		return make(map[int64]*TeamUser), nil
 	}
 	ownerTeam, err := GetOwnerTeam(ctx, orgID)
 	if err != nil {
 		if IsErrTeamNotExist(err) {
 			log.Error("Organization does not have owner team: %d", orgID)
-			return nil, nil
+			return make(map[int64]*TeamUser), nil
 		}
 		return nil, err
 	}