[TTS] [bugfix] German FastPitch HiFi-GAN tutorial and lr
# What does this PR do ?

Address QA bugs for German TTS tutorial. Correct PR instead of https://github.com/NVIDIA/NeMo/pull/4449 

**Collection**: TTS

# Changelog 
- tutorial notebook changed
- learning rate updated to 1e-3 based on https://github.com/NVIDIA/NeMo/pull/4308 

**PR Type**: Bugfix
