fast_dev_run breaks with val_check_interval
🐛 Bug
It looks like val_check_interval must be <= num_training_batches, but the latter is set to 1 in fast_dev_run, so things break.
Please reproduce using the BoringModel
https://colab.research.google.com/drive/1cMWbhk5pmkGe_y6znQFHebRUrqa_ssu9?usp=sharing
To Reproduce
Use following BoringModel and post here

Expected behavior
Probably validation checks should be disabled in fast_dev_run Or val_check_interval should be set to 1 as well.
Environment

CUDA:

GPU:

Tesla T4


available:         True
version:           10.1


Packages:

numpy:             1.19.5
pyTorch_debug:     True
pyTorch_version:   1.7.0+cu101
pytorch-lightning: 1.1.4
tqdm:              4.41.1


System:

OS:                Linux
architecture:

64bit



processor:         x86_64
python:            3.6.9
version:           #1 SMP Thu Jul 23 08:00:38 PDT 2020



Additional context