**Apache Airflow version**: 2.0.0


**Kubernetes version (if you are using kubernetes)** (use `kubectl version`): N/A

**Environment**: 

- **Cloud provider or hardware configuration**: local/aws
- **OS** (e.g. from /etc/os-release): Ubuntu 18.04.5 LTS
- **Kernel** (e.g. `uname -a`): 5.4.0-1032-aws
- **Install tools**: pip
- **Others**:

**What happened**:
I did a fresh Airflow 2.0.0 install. With this version, when I manually trigger a DAG, Airflow skips the next scheduled run.
<!-- (please include exact error messages if you can) -->

**What you expected to happen**:
Manual runs do not interfere with the scheduled runs prior to Airflow 2. 
<!-- What do you think went wrong? -->

**How to reproduce it**:
Create a simple hourly DAG. After enabling it and the initial run, run it manually. It shall skip the next hour. Below is an example, where the manual run with execution time of 08:17 causes the scheduled run with execution time of 08:00 to skip. 
![image](https://user-images.githubusercontent.com/26160471/103457719-c7193480-4d12-11eb-82cb-42efaedc9ef4.png)


airflow/models/dag.py
"""
        Get the Default DAG View, returns the default config value if DagModel does not
        have a value
        """
        
        return self.default_view or conf.get('webserver', 'dag_default_view').lower()
    @property
    def safe_dag_id(self):
        return self.dag_id.replace('.', '__dot__')
    @provide_session
    def set_is_paused(self, is_paused: bool, including_subdags: bool = True, session=None) -> None:
        """
        Pause/Un-pause a DAG.
        :param is_paused: Is the DAG paused
        :param including_subdags: whether to include the DAG's subdags
        :param session: session
        """
        filter_query = [
            DagModel.dag_id == self.dag_id,
        ]
        if including_subdags:
            filter_query.append(DagModel.root_dag_id == self.dag_id)
        session.query(DagModel).filter(or_(*filter_query)).update(
            {DagModel.is_paused: is_paused}, synchronize_session='fetch'
        )
        session.commit()
    @classmethod
    @provide_session
    def deactivate_deleted_dags(cls, alive_dag_filelocs: List[str], session=None):