[TASK] Fix Upgrade.mx

Upgrade.md

 # Upgrade from ```9.x.x``` to ```10.x.x```
 
 - Dropped TYPO3 9 support
+- Dropped php 7.3 support
 - enableAutomaticRelatedNews defaults now to 1 instead of 0
 
 ## Upgrade from ```9.5.x``` to ```9.6.x```