GAN Manual Optimization not working for 1.2.0 through master
🐛 Bug
Originally #5545 but since the problem appears to have been fixed and then re-appeared, I thought I'd just create another issue.
Please reproduce using the BoringModel

https://colab.research.google.com/gist/import-antigravity/0730243bb11b56031110fd6aa7d58971/the-boringmodel.ipynb
To Reproduce
Alter the ! pip command at the beginning of the notebook to change the version and observe that after 1.2.0 the GAN does not appear to begin to converge, and just outputs noise. Running the code on version 1.1.8 works.
Expected behavior
After running the code for 5 epochs it should be clear that the GAN is beginning to create the MNIST digits.
Environment
* CUDA:
	- GPU:
		- Tesla T4
	- available:         True
	- version:           10.1
* Packages:
	- numpy:             1.19.5
	- pyTorch_debug:     False
	- pyTorch_version:   1.7.1+cu101
	- pytorch-lightning: 1.3.0dev
	- tqdm:              4.41.1
* System:
	- OS:                Linux
	- architecture:
		- 64bit
		- 
	- processor:         x86_64
	- python:            3.7.10
	- version:           #1 SMP Thu Jul 23 08:00:38 PDT 2020
	```