Fix MorphTo Model Doc Generation

[yparitcher]

fix:

    /**
     * @return MorphTo<contravariant ModelA|ModelB, $this>
     */
    public function reminderable(): MorphTo {
        return $this->morphTo(__FUNCTION__, 'entity', 'entity_id');
    }

From:

* @property-read contravariant ModelA|ModelB $reminderable

To:

* @property-read ModelA|ModelB $reminderable ``` Fixes: #1667

## Summary
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## Type of change

<!-- Please delete options that are not relevant. -->

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
- [ ] This change requires a documentation update
- [ ] Misc. change (internal, infrastructure, maintenance, etc.)

### Checklist
- [ ] Existing tests have been adapted and/or new tests have been added
- [ ] Update the README.md
- [ ] Code style has been fixed via `composer fix-style`