Changing the type of a public variable with an assignment from GameObject to Transform or the other way around does not give a type mismatch error.

Repro steps:
1. Open Scene1 from attached project.
2. Open Assignment script and change the type of 'go' to GameObject
3. Select Cube in scene and in its assignment script assign the same cube to the `go` variable.
4. Go back in the script and change the type of `go` to `Transform`
5. Select the Cube in the scene again and observe that it is still referencing the game object.
6. Assign the cube again to the same `go` slow and observe how the icon is changing.

Expected outcome: to get a type mismatch (if the type of 'go' is changed to LineRenderer for example, inspector will show type mismatch)

Notes:
- Not a regression, repros in 5.5.0b1 and in 5.4.1f1
- Attached gif shows process
- Attached jpg shows expected result when using a different type (LineRenderer in this case)