Fabric API – [1.20.1] Fabric API 0.86.1+1.20.1

– Bump version (modmuss50)
– Fix data generation for custom dynamic registry (#3216) (apple502j, modmuss50)
– Clarify nullability of `ModelModifier.AfterBake` (#3212) (PepperCode1)
– Fix #3215 – Only add namespace to registries added using the Fabric API. (#3219) (modmuss)
– Sort item groups to ensure they are in a deterministic order between runs. (#3222) (modmuss)